Vehicle travel control apparatus

ABSTRACT

A vehicle travel control apparatus includes an actuator and an electronic control unit. The electronic control unit is configured to determine whether a driver of a vehicle is in an abnormal state where the driver loses an ability of driving the vehicle. The electronic control unit is also configured to stop the vehicle at an abnormality determination time point onward, and control a vehicle speed by using the actuator such that the vehicle speed does not become lower than a lower limit vehicle speed in a period from the abnormality determination time point to a time point when the vehicle is stopped. The lower limit vehicle speed is set in accordance with a road shape influencing timing when a driver of another vehicle traveling behind the vehicle visually recognizes the vehicle.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2016-080454 filed onApr. 13, 2016 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The disclosure relates to a vehicle travel control apparatus.

2. Description of Related Art

A device that determines whether a driver falls in an abnormal statewhere the driver loses an ability of driving a vehicle (for example, adrowsy driving state, a mental and physical function stopped state, orthe like) and decelerates the vehicle when such a determination is madehas been proposed (for example, see Japanese Patent ApplicationPublication No. 2009-73462 (JP 2009-73462 A)). Note that hereinafter the“abnormal state where the driver loses the ability of driving thevehicle” will also simply be referred to as a “driving incapableabnormal state” and the “determination on whether the driver is in thedriving incapable abnormal state” will also simply be referred to as a“driver abnormality determination”.

SUMMARY

According to the conventional device, in the case where it is determinedthat the driver falls in the driving incapable abnormal state, thevehicle continues to be decelerated, and a vehicle speed is reduced alsoin a region with poor visibility due to a road shape, like a pointimmediately after the vehicle passes a curved road and a pass, forexample. As a result, a driver in a vehicle behind may have to abruptlybrake to avoid a collision when recognizing the vehicle.

The disclosure provides a vehicle travel control apparatus that reducesa vehicle speed when it is determined that a driver falls in a drivingincapable abnormal state and that does not reduce the vehicle speedexcessively when a vehicle travels in a region with poor visibility dueto a road shape.

An aspect of the disclosure provides a vehicle travel control apparatus.The vehicle travel control apparatus according to the aspect includes atleast one actuator and at least one electronic control unit. The atleast one electronic control unit is configured to determine whether adriver of a vehicle is in an abnormal state where the driver loses anability of driving the vehicle. The at least one electronic control unitis configured to stop the vehicle at an abnormality determination timepoint onward, the abnormality determination time point being a timepoint at which it is determined that the driver is in the abnormalstate, and control a vehicle speed of the vehicle by using the at leastone actuator such that the vehicle speed does not become lower than alower limit vehicle speed, in a period from the abnormalitydetermination time point to a time point at which the vehicle isstopped. The lower limit vehicle speed is set in accordance with a roadshape influencing timing at which a driver of another vehicle travelingbehind the vehicle visually recognizes the vehicle, among shapes of theroad on which the vehicle travels.

According to the above, the vehicle speed of the deceleration targetvehicle can be controlled such that the vehicle speed of thedeceleration target vehicle is not excessively reduced (does not becomelower than the lower limit vehicle speed) in the case where thedeceleration target vehicle travels on the road with the poor visibility(such a road that the timing at which the driver of the vehicle behindthe deceleration target vehicle visually recognizes the decelerationtarget vehicle is delayed in comparison with the timing on a straightand flat road). As a result of this, a possibility that the driver ofthe vehicle behind who recognizes the deceleration target vehicle has toabruptly brake the vehicle behind can be reduced.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain information on the road shape, and maybe configured to set the lower limit vehicle speed based on theinformation on the road shape.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain information on a radius of curvature ofthe road at a point ahead of a point at which the vehicle travels at acurrent time point as the information on the road shape, and may beconfigured to set the lower limit vehicle speed to a higher value as theradius of curvature indicated by the info, illation on the radius ofcurvature is reduced.

According to the above, the radius of curvature of the road at the pointahead of the deceleration target vehicle can be obtained before thevehicle reaches the point ahead. Thus, the vehicle speed of thedeceleration target vehicle can be controlled in advance such that thevehicle speed of the deceleration target vehicle does not fall below thelower limit vehicle speed. Furthermore, there is a tendency that thetiming at which the driver of the vehicle behind recognizes thedeceleration target vehicle is delayed as the radius of curvature isreduced. Thus, the lower limit vehicle speed is set to the higher valueas the radius of curvature is reduced. As a result of this, thepossibility that the driver of the vehicle behind who recognizes thedeceleration target vehicle has to abruptly brake the vehicle behind canfurther be reduced.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain the radius of curvature or thecurvature of at least one section of the road as information on theradius of curvature of the road from a map database, and may beconfigured to set the lower limit vehicle speed for each of the sectionbased on the radius of curvature or the curvature of each of thesection. The at least one electronic control unit may be configured todetermine a particular point reaching time point. The particular pointreaching time point may be determined such that the vehicle speed of thevehicle in a period from the particular point reaching time point to thetime point at which the vehicle is stopped does not become lower thanthe lower limit vehicle speed, the particular point reaching time pointbeing at which the vehicle reaches a particular point ahead of aposition at the abnormality determination time point, the lower limitvehicle speed being set for each of the section, when the vehiclereaches the particular point reaching time point while keeping a vehiclespeed at the abnormality determination time point, and the vehicle isdecelerated at constant deceleration from the particular point reachingtime point. The at least one electronic control unit may be configuredto make the vehicle travel at the vehicle speed at the abnormalitydetermination time point, from the abnormality determination time pointto the particular point reaching time point, and may be configured todecelerate the vehicle at the constant deceleration by using the atleast one actuator from the particular point reaching time point.

When the map database is used as described above, it is possible toestimate in advance the road (the section of the road) with what kind ofradius of curvature the deceleration target vehicle travels (in otherwords, how the lower limit vehicle speed is changed) until thedeceleration target vehicle stops. Accordingly, the position at whichthe deceleration starts (the particular point) can be determined beforestarting of the deceleration in the case where the deceleration targetvehicle is decelerated at the constant deceleration.

Furthermore, according to this aspect, the deceleration target vehicleis decelerated while the constant deceleration is kept. Suchdeceleration of keeping the constant deceleration differs fromdeceleration during vehicle speed automatic control in normal ACC (willbe described below) or the like. Accordingly, occupants including thedriver of the deceleration target vehicle can receive a sense ofdiscomfort. Thus, if the driver is not in the driving incapable abnormalstate, the driver and passenger, if the passenger exists, can recognizethat the vehicle is forcibly decelerated. In addition, because thedeceleration does not fluctuate, a possibility that the driver of theother vehicle traveling around the deceleration target vehicle has toperform a special drive operation such as abrupt braking or abruptsteering can be reduced. Note that this effect is an effect exerted in asimilar manner in another aspect of the disclosure in which thedeceleration target vehicle is decelerated while keeping the constantdeceleration.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain the radius of curvature or thecurvature of at least one section of the road as the information on theradius of curvature of the road from a map database, and may beconfigured to set the lower limit vehicle speed for each of the sectionbased on the radius of curvature or the curvature of each of thesection. The at least one electronic control unit may be configured todetermine constant deceleration such that the vehicle speed of thevehicle in the period from the abnormality determination time point tothe time point at which the vehicle is stopped does not become lowerthan the lower limit vehicle speed set for each of the section when thevehicle is decelerated at the constant deceleration by using the atleast one actuator from the abnormality determination time point, andmay be configured to decelerate the vehicle at the constant decelerationfrom the abnormality determination time point.

As described above, by using the map database, it is possible toestimate in advance how the lower limit vehicle speed is changed untilthe deceleration target vehicle is stopped. Accordingly, before a startof the deceleration, it can be determined at what constant decelerationthe deceleration target vehicle should be decelerated from theabnormality determination time point in order to prevent the vehiclespeed of the deceleration target vehicle from becoming lower than thelower limit vehicle speed, which is set per the section of the road,until the time point at which the vehicle stops.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain the radius of curvature or thecurvature of at least one section as the information on the radius ofcurvature of the road from a map database. The at least one electroniccontrol unit may be configured to set the lower limit vehicle speed foreach of the section based on the radius of curvature or the curvature ofeach of the section. The at least one electronic control unit may beconfigured to decelerate the vehicle at constant deceleration at theabnormality determination time point onward, and temporarily interruptdeceleration of the vehicle and keep the vehicle speed of the vehicle ina period in which it is predicted that the vehicle speed of the vehiclebecomes lower than the lower limit vehicle speed set for each of thesection, the period being in the period from the abnormalitydetermination time point to the time point at which the vehicle isstopped.

According to the above, the vehicle speed of the deceleration targetvehicle can be prevented from falling below the lower limit vehiclespeed, and the deceleration of the deceleration target vehicle can becontinued when the vehicle speed of the deceleration target vehicle ishigher than the lower limit vehicle speed. Accordingly, the vehiclespeed of the deceleration target vehicle can be reduced as much aspossible while the vehicle speed of the deceleration target vehicle isprevented from falling below the lower limit vehicle speed.

In the aspect of the disclosure, the vehicle travel control apparatusaccording to the aspect may further include a camera device that obtainsimage data by capturing an image in front of the vehicle. The at leastone electronic control unit may be configured to obtain the radius ofcurvature or the curvature of the road at a particular point ahead of aposition of the vehicle at the current time point by a specifieddistance as the information on the radius of curvature of the road basedon the image data, and may be configured to set the lower limit vehiclespeed based on the radius of curvature or the curvature at theparticular point. In the case where it is predicted that the vehiclespeed at a time when the vehicle reaches the particular point becomeslower than the lower limit vehicle speed when the vehicle is deceleratedat constant deceleration from the abnormality determination time pointonward, the at least one electronic control unit may be configured tomake the vehicle travel at a constant speed so as to keep the vehiclespeed of the vehicle at a time point when the vehicle speed ispredicted, in the case where the vehicle speed of the vehicle at thetime point when the vehicle speed is predicted is equal to or higherthan the lower limit vehicle speed at the particular point, and may beconfigured to accelerate the vehicle by using the at least one actuatorsuch that the vehicle speed of the vehicle becomes equal to or higherthan the lower limit vehicle speed at the particular point before thevehicle reaches the particular point in the case where the vehicle speedof the vehicle at the time point when the vehicle speed is predicted islower than the lower limit vehicle speed at the particular point.

According to the above, for example, even when the information of themap database cannot be used, even when the information of the mapdatabase is old information, or the like, the vehicle speed of thedeceleration target vehicle can be gradually reduced while the vehiclespeed of the deceleration target vehicle is prevented from significantlyfalling below the lower limit vehicle speed.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain information on a radius of curvature ofthe road at a point at which the vehicle travels at a current time pointas the information on the road shape, and may be configured to set thelower limit vehicle speed to a higher value as the radius of curvatureindicated by the information on the radius of curvature is reduced.

According to the above, the lower limit vehicle speed at the currenttime point is set to the higher value as the radius of curvature of theroad at the point at which the deceleration target vehicle travels atthe current time point is reduced. Accordingly, the vehicle speed of thedeceleration target vehicle can be controlled such that the vehiclespeed of the deceleration target vehicle at the current time point doesnot fall below the lower limit vehicle speed of the road on which thedeceleration target vehicle travels at the current time point.

In the aspect of the disclosure, the vehicle travel control apparatusaccording to the aspect may further include a camera device that obtainsimage data by capturing an image in front of the vehicle. The at leastone electronic control unit may be configured to obtain the radius ofcurvature or the curvature of the road at the point at which the vehicletravels at the current time point as the information on the radius ofcurvature of the road based on the image data. The at least oneelectronic control unit may be configured to decelerate the vehicle whenthe vehicle speed of the vehicle at the current time point is higherthan the lower limit vehicle speed at the point at which the vehicletravels at the current time point, and the at least one electroniccontrol unit may be configured to accelerate the vehicle by using the atleast one actuator such that the vehicle speed of the vehicle becomesequal to or higher than the lower limit vehicle speed, when the vehiclespeed of the vehicle at the current time point is lower than the lowerlimit vehicle speed at the point at which the vehicle travels at thecurrent time point.

According to the above, the vehicle speed of the deceleration targetvehicle at the current time point can be controlled on the basis of theimage data obtained by the camera device such that the vehicle speed ofthe deceleration target vehicle does not fall below the lower limitvehicle speed of the road on which the deceleration target vehicletravels at the current time point.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain information on a grade change amount ofthe road as the information on the road shape, and set the lower limitvehicle speed to a higher value as the grade change amount at a point ofa pass, the point of the pass being indicated by the information on thegrade change amount, is increased.

In the case where the deceleration target vehicle travels by passing thepass in which a grade of the road is changed from an up grade to a downgrade, timing at which the driver of the vehicle behind recognizes thedeceleration target vehicle is delayed longer as the grade change amount(dI) before and after the pass is increased. Accordingly, when the lowerlimit vehicle speed is set on the basis of the grade change amount as inthe above aspect, the possibility that the driver of the vehicle behindwho recognizes the deceleration target vehicle traveling by passing thepass has to abruptly brake the vehicle behind can be reduced.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain the information on the grade changeamount from a map database, and may be configured to set the lower limitvehicle speed to a higher value as the grade change amount is increased.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to obtain a travel distance for which the vehicletravels after passing the point of the pass, and may be configured toset the lower limit vehicle speed to a higher value as the traveldistance is reduced.

According to the above, speed control of the deceleration target vehiclecan be executed such that the vehicle speed of the deceleration targetvehicle of a case where the deceleration target vehicle travels in aregion near the point of the pass becomes higher than the vehicle speedof the deceleration target vehicle of a case where the decelerationtarget vehicle travels in a region far from the point of the pass. Thus,the possibility that the driver of the vehicle behind who recognizes thedeceleration target vehicle has to abruptly brake the vehicle behind canfurther be reduced.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to determine that the driver of the vehicle is inthe abnormal state when the driver of the vehicle does not perform apredetermined operation for a longer time than a predetermined time.

In the aspect of the disclosure, the at least one electronic controlunit may be configured to determine that the driver of the vehicle is inthe abnormal state when the driver of the vehicle does not perform adrive operation for the longer time than the predetermined time.

In the aspect of the disclosure, the vehicle travel control apparatusaccording to the aspect may further include a confirmation buttonmounted on the vehicle. The at least one electronic control unit may beconfigured to make notification of urging the driver of the vehicle tooperate the confirmation button and may be configured to determine thatthe driver of the vehicle is in the abnormal state when the driver ofthe vehicle does not operate the confirmation button for a predeterminedtime after the notification is made.

In the above description, in order to facilitate understanding of thedisclosure, components of the disclosure that correspond to those ofembodiments, which will be described below, are each added with a nameand/or a reference numeral used in the embodiment in a parenthesis.However, each of the components of the disclosure is not limited to thatof the embodiments defined by the name and/or the reference numeral.Other purposes, other features, and accompanying advantages of thedisclosure will easily be understood from the description of theembodiments of the disclosure with reference to drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a schematic configuration diagram of a vehicle travel controlapparatus (a first apparatus) according to a first embodiment of thedisclosure;

FIG. 2A is a time chart for explaining actuation of the first apparatus;

FIG. 2B is a time chart for explaining the actuation of the firstapparatus;

FIG. 3 is a flowchart of a routine that is executed by a CPU of thefirst apparatus;

FIG. 4 is a flowchart of a routine that is executed by the CPU of thefirst apparatus;

FIG. 5 is a flowchart of a routine that is executed by the CPU of thefirst apparatus;

FIG. 6 is a time chart for explaining actuation of a vehicle travelcontrol apparatus (a second apparatus) according to a second embodimentof the disclosure;

FIG. 7 is a flowchart of a routine that is executed by a CPU of thesecond apparatus;

FIG. 8 is a time chart for explaining actuation of a vehicle travelcontrol apparatus (a third apparatus) according to a third embodiment ofthe disclosure;

FIG. 9 is a flowchart of a routine that is executed by a CPU of thethird apparatus;

FIG. 10A is a time chart for explaining actuation of a vehicle travelcontrol apparatus (a fourth apparatus) according to a fourth embodimentof the disclosure;

FIG. 10B is a time chart for explaining the actuation of the vehicletravel control apparatus (the fourth apparatus) according to the fourthembodiment of the disclosure;

FIG. 10C is a time chart for explaining the actuation of the vehicletravel control apparatus (the fourth apparatus) according to the fourthembodiment of the disclosure;

FIG. 10D is a time chart for explaining the actuation of the vehicletravel control apparatus (the fourth apparatus) according to the fourthembodiment of the disclosure;

FIG. 11A is a time chart for explaining the actuation of the vehicletravel control apparatus (the fourth apparatus) according to the fourthembodiment of the disclosure;

FIG. 11B is a time chart for explaining the actuation of the vehicletravel control apparatus (the fourth apparatus) according to the fourthembodiment of the disclosure;

FIG. 11C is a time chart for explaining the actuation of the vehicletravel control apparatus (the fourth apparatus) according to the fourthembodiment of the disclosure;

FIG. 11D is a time chart for explaining the actuation of the vehicletravel control apparatus (the fourth apparatus) according to the fourthembodiment of the disclosure;

FIG. 12 is a flowchart of a routine that is executed by a CPU of thefourth apparatus;

FIG. 13 is a flowchart of a routine that is executed by a CPU of avehicle travel control apparatus (a fifth apparatus) according to afifth embodiment of the disclosure;

FIG. 14 is a flowchart of a routine that is executed by a CPU of avehicle travel control apparatus according to a modified example of thefifth embodiment of the disclosure;

FIG. 15 is a flowchart of a routine that is executed by a CPU of avehicle travel control apparatus (a sixth apparatus) according to asixth embodiment of the disclosure; and

FIG. 16 is a flowchart of a routine that is executed by a CPU of avehicle travel control apparatus (a seventh apparatus) according to aseventh embodiment of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

A description will hereinafter be made on a vehicle travel controlapparatus (a drive assist system) according to each embodiment of thedisclosure with reference to the drawings.

First Embodiment

As shown in FIG. 1, a vehicle travel control apparatus according to afirst embodiment of the disclosure (hereinafter may also referred to asa “first apparatus”) is applied to a vehicle (hereinafter may also bereferred to as a “host vehicle” to be distinguished from other vehicles)and includes a drive assist ECU 10, a navigation ECU 20, an engine ECU30, a brake ECU 40, an electric parking brake ECU 50, a steering ECU 60,a meter ECU 70, and an Mann ECU 80.

These ECUs are each an electric control unit that includes amicrocomputer as a main component, are mutually connected to be able totransmit and receive information via a controller area network (CAN),which is not shown. In this specification, the microcomputer includes aCPU, ROM, RAM, non-volatile memory, an interface I/F, and the like. TheCPU executes instructions (programs, routines) stored in the ROM torealize various functions. Some or all of these ECUs may be integratedinto one ECU.

The drive assist ECU 10 is connected to sensors (including switches),which will be listed below, and receives detection signals or outputsignals of those sensors. Note that each of the sensors may be connectedto any of the ECUs other than the drive assist ECU 10. In such a case,the drive assist ECU 10 receives the detection signal or the outputsignal of the sensor from the ECU, to which the sensor is connected, viathe CAN.

An accelerator pedal operation amount sensor 11 detects an operationamount (an accelerator opening degree) of an accelerator pedal 11 a ofthe host vehicle and outputs a signal indicative of an accelerator pedaloperation amount AP. A brake pedal operation amount sensor 12 detects anoperation amount of a brake pedal 12 a of the host vehicle and outputs asignal indicative of a brake pedal operation amount BP. A stop lampswitch 13 outputs a low-level signal when the brake pedal 12 a is notdepressed (not operated), and outputs a high-level signal when the brakepedal 12 a is depressed (operated).

A steering angle sensor 14 detects a steering angle of the host vehicleand outputs a signal indicative of a steering angle θ. A steering torquesensor 15 detects steering torque that is applied to a steering shaft USof the host vehicle through an operation of a steering wheel SW, andoutputs a signal indicative of steering torque Tra. A vehicle speedsensor 16 detects a traveling speed of the host vehicle (a vehiclespeed) and outputs a signal indicative of a vehicle speed SPD.

A radar sensor 17 a obtains information on a front road of the hostvehicle and stereoscopic objects on the road. The stereoscopic objectsinclude, for example, moving objects such as a pedestrian, a bicycle,and an automobile, and fixed objects such as a utility pole, a tree, anda guardrail. Hereinafter, these stereoscopic objects may each bereferred to as a “target object”.

The radar sensor 17 a includes “a radar transmission/reception sectionand a signal processing section”, neither of which is shown. The radartransmission/reception section emits a radio wave of a millimeter-waveband (hereinafter referred to as a “millimeter wave”) to a peripheralregion of the host vehicle that includes a front region of the hostvehicle, and receives the millimeter wave that is reflected by thetarget object existing in a radiation range (that is, a reflected wave).Based on a phase difference between the transmitted millimeter wave andthe received reflected wave, an attenuation level of the reflected wave,a time from transmission of the millimeter wave to reception of thereflected wave, and the like, the signal processing section obtains aninter-vehicular distance (a longitudinal distance) Dfx(n), a relativespeed Vfx(n), a horizontal distance Dfy(n), a relative horizontal speedVfy(n), and the like with respect to each detected target object (n)every time a specified time elapses.

The inter-vehicular distance Dfx(n) is a distance between the hostvehicle and the target object (n) (for example, a preceding vehicle)along a center axis of the host vehicle. The relative speed Vfx(n) is adifference (=Vs−Vj) between a speed Vs of the target object (n) (forexample, the preceding vehicle) and a speed Vj of a host vehicle VA. Thespeed Vs of the target object (n) is a speed of the target object (n) ina traveling direction of the host vehicle. The horizontal distanceDfy(n) is a distance of a “center position of the target object (n) (forexample, a center position in vehicle width of the preceding vehicle)”from the center axis of the host vehicle in a direction that isorthogonal to the center axis. The horizontal distance Dfy(n) will alsobe referred to as a “horizontal position”. The relative horizontal speedVfy(n) is a speed at the center position of the target object (n) (forexample, the center position in vehicle width of the preceding vehicle)in the direction that is orthogonal to the center axis of the hostvehicle.

A camera device 17 b includes “a stereo camera and an image processingsection”, neither of which is shown. The stereo camera obtains a rightand left pair of image data by capturing scenery of a left region and aright region in front of the vehicle. Based on the right and left pairof the image data captured by the stereo camera, the image processingsection calculates and outputs presence or absence of the target object,a relative relationship between the host vehicle and the target object,and the like.

Note that the drive assist ECU 10 determines the relative relationshipbetween the host vehicle and the target object (target objectinformation) by synthesizing the relative relationship between the hostvehicle and the target object obtained by the radar sensor 17 a and therelative relationship between the host vehicle and the target objectobtained by the camera device 17 b. Furthermore, based on the right andleft pair of the image data (road image data) captured by the cameradevice 17 b, the drive assist ECU 10 recognizes lane markers(hereinafter simply referred to as “lane lines”), such as right and leftlane lines, on the road and obtains a road shape (a radius of curvatureindicative of a degree of curvature of the road), a positionalrelationship between the road and the vehicle, and the like. Moreover,based on the road image data captured by the camera device 17 b, thedrive assist ECU 10 can obtain information on whether a roadside wallexists.

An operation switch 18 is a switch operated by a driver. The driver canselect whether to execute lane keeping assist control (LKA) by operatingthe operation switch 18. Furthermore, the driver can select whether toexecute adaptive cruise control (ACC) by operating the operation switch18.

A yaw rate sensor 19 detects a yaw rate of the host vehicle and outputsan actual yaw rate YRa.

The drive assist ECU 10 can execute the LKA and the ACC. Furthermore, aswill be described below, the drive assist ECU 10 determines whether thedriver is in an abnormal state where the driver loses the ability ofdriving the vehicle (a driving incapable abnormal state), and executesvarious types of control including the lane keeping assist control whendetermining that the driver is in the driving incapable abnormal state.

The navigation ECU 20 is connected to a GPS receiver 21 that receives aGPS signal for detecting a position of the host vehicle, a map database22 that stores map information and the like, a touch panel display 23 asa human-machine interface, and the like. The navigation ECU 20identifies a position Pnow at a current time point (a current position)of the host vehicle on the basis of the GPS signal, performs varioustypes of arithmetic processing on the basis of the position Pnow of thehost vehicle, the map information stored in the map database 22, and thelike, and guides the driver through a route by using the display 23.

The map information stored in the map database 22 includes roadinformation. The road information includes a parameter that indicatesthe road shape per section of the road (for example, the radius ofcurvature of the road indicative of the degree of curvature of the roador curvature). Note that the curvature is inverse of the radius ofcurvature.

The engine ECU 30 is connected to an engine actuator 31. The engineactuator 31 is an actuator that changes an operation state of aninternal combustion engine 32. In this example, the internal combustionengine 32 is a multi cylinder engine of a gasoline fuel injection, sparkignition type and includes a throttle valve for adjusting an intake airamount. The engine actuator 31 at least includes a throttle valveactuator that changes an opening degree of the throttle valve. Theengine ECU 30 can change torque that is generated by the internalcombustion engine 32 by driving the engine actuator 31. The torquegenerated by the internal combustion engine 32 is transmitted tounillustrated drive wheels via an unillustrated transmission.Accordingly, the engine ECU 30 can control drive power of the hostvehicle to change an accelerated state (acceleration) by controlling theengine actuator 31.

The brake ECU 40 is connected to a brake actuator 41. The brake actuator41 is provided in a hydraulic circuit between a master cylinder, whichis not shown, and a friction brake mechanism 42, the master cylinderpressurizes hydraulic oil by a depression force of a brake pedal, andthe friction brake mechanism 42 is provided on each of right and leftfront and rear wheels. The friction brake mechanism 42 includes a brakedisc 42 a fixed to the wheel and a brake caliper 42 b fixed to a vehiclebody. The brake actuator 41 adjusts hydraulic pressure that is suppliedto a wheel cylinder housed in the brake caliper 42 b in accordance withan instruction from the brake ECU 40 and actuates the wheel cylinder bythe hydraulic pressure. In this way, a brake pad is pressed against thebrake disc 42 a to generate a friction braking force. Thus, the brakeECU 40 can control a braking force of the host vehicle by controllingthe brake actuator 41.

The electric parking brake ECU (hereinafter may be referred to as an“EPB ECU”) 50 is connected to a parking brake actuator (hereinafter maybe referred to as a “PKB actuator”) 51. The PKB actuator 51 is anactuator that presses the brake pad against the brake disc 42 a or thatpresses a shoe against a drum when a drum brake is provided, and thedrum rotates with the wheel. Thus, the EPB ECU 50 applies a parkingbraking force to each of the wheels by using the PKB actuator 51 andthus can keep the vehicle in a stopped state.

The steering ECU 60 is a control unit of a well-known electric powersteering system and is connected to a motor driver 61. The motor driver61 is connected to a steering motor 62. The steering motor 62 isembedded in an unillustrated “steering mechanism that includes thesteering wheel, the steering shaft coupled to the steering wheel, asteering gear mechanism, and the like” of the vehicle. The steeringmotor 62 generates torque by electric power supplied from the motordriver 61, can add steering assist torque by this torque, and can turnright and left turning wheels.

The meter ECU 70 is connected to an unillustrated digital display typemeter and is also connected to a hazard lamp 71 and a stop lamp 72. Themeter ECU 70 can flash the hazard lamp 71 and light the stop lamp 72 inaccordance with an instruction from the drive assist ECU 10.

The alarm ECU 80 is connected to a buzzer 81 and an indicator 82. Inaccordance with an instruction from the drive assist ECU 10, the alarmECU 80 can sound the buzzer 81 to alert the driver, light an alert mark(for example, a warning lamp), display a warning message, and display anactuation condition of drive assist control on the indicator 82.

Furthermore, the drive assist ECU 10 is connected to a confirmationbutton 90. The confirmation button 90 is disposed at a position wherethe driver can operate the confirmation button 90, outputs a low-levelsignal when not being operated, and outputs a high-level signal whenbeing pressed for an operation.

(Overview of Actuation) Next, a description will be made on primaryactuation of the drive assist ECU 10 (hereinafter also simply referredto as the “ECU 10”) according to the first apparatus. The ECU 10determines whether the driver is in “the abnormal state where the driverloses the ability of driving the vehicle (the driving incapable abnormalstate)” by using one of various methods, which will be described below.For example, in the case where the vehicle speed SPD of the host vehicleis equal to or higher than a specified vehicle speed SPDth, the ECU 10determines (monitors) whether a non-operating state where none of “theaccelerator pedal operation amount AP, the brake pedal operation amountBP, and the steering torque Tra” is changed (a state where a driveoperation is not performed) continues for an abnormality determinationthreshold time or longer. When the non-operating state continues for theabnormality determination threshold time or longer, it is determinedthat the driver is in the driving incapable abnormal state (such adetermination that the driver falls in the driving incapable abnormalstate is confirmed).

The ECU 10 executes the lane keeping assist control (LKA) whendetermining that the driver is in the driving incapable abnormal state.The lane keeping assist control is control for applying the steeringtorque to the steering mechanism so as to assist a steering operation bythe driver such that the position of the host vehicle is kept near atarget travel line within “a lane (a traveling lane) in which the hostvehicle travels”. The lane keeping assist control itself has been wellknown (for example, see Japanese Patent Application Publication No.2008-195402 (JP 2008-195402 A), Japanese Patent Application PublicationNo. 2009-190464 (JP 2009-190464 A), Japanese Patent ApplicationPublication No. 2010-6279 (JP 2010-6279 A), the specification ofJapanese Patent No. 4349210, and the like). Thus, the lane keepingassist control will briefly be described below.

More specifically, based on the image data transmitted from the cameradevice 17 b, the ECU 10 recognizes (obtains) “a left lane line LL and aright lane line LR” of the lane, on which the host vehicle travels, anddetermines a central position between those paired lane lines as atarget travel line Ld. Furthermore, the ECU 10 calculates: a curveradius (a radius of curvature) R of the target travel line Ld; and theposition and a direction of the host vehicle on the traveling lane,which is defined by the left lane line LL and the right lane line LR.

Then, the ECU 10 calculates: a distance Dc (hereinafter referred to as a“center distance Dc”) in a road width direction between a front endcentral position of the host vehicle and the target travel line Ld; anda deviation angle θy (hereinafter referred to as a “yaw angle θy”)between a direction of the target travel line Ld and the travelingdirection of the host vehicle.

Furthermore, based on the center distance Dc, the yaw angle θy, and roadcurvature ν (=1/the radius R of curvature), the ECU 10 calculates atarget yaw rate YRc* by the following equation (1) in a specifiedcalculation cycle. In the equation (1), K1, K2, and K3 are controlgains. The target yaw rate YRc* is a yaw rate that is set to allow thehost vehicle to travel along the target travel line Ld.

YRc*=K1×Dc+K2×θy+K3×ν  (1)

Based on this target yaw rate YRc* and the actual yaw rate YRa, the ECU10 calculates target steering torque Tr* for obtaining the target yawrate YRc* in the specified calculation cycle. More specifically, the ECU10 stores a lookup table in advance, the lookup table defining arelationship between the target steering torque Tr* and a deviationbetween the target yaw rate YRc* and the actual yaw rate YRa. Then, theECU 10 calculates the target steering torque Tr* by applying thedeviation between the target yaw rate YRc* and the actual yaw rate YRato this table. Thereafter, the drive assist ECU 10 controls the steeringmotor 62 by using the steering ECU 60 such that the actual steeringtorque Tra matches the target steering torque Tr*. What has beendescribed above is the overview of the lane keeping assist control.

In addition, when determining that the driver is in the drivingincapable abnormal state, as shown in FIG. 2A and FIG. 2B, the ECU 10computes a required stop distance (=SPDnow²/(2·|Dec|) that is a distanceuntil a stop of the host vehicle (the vehicle speed SPD=0) bydecelerating the host vehicle from a current vehicle speed SPDnow of thehost vehicle at constant deceleration Dec. In the case where the hostvehicle is decelerated from the current vehicle speed SPDnow at theconstant deceleration Dec, the ECU 10 computes a vehicle speed SPD(px)of the host vehicle at a point px at which the host vehicle reachesafter traveling for a distance x from a current position Pnow.

The ECU 10 identifies a position Pstop at which the host vehicle stopsfrom the current position Pnow and the required stop distance of thehost vehicle. The ECU 10 obtains information on the road shape betweenthe current position Pnow and the stop position Pstop from the mapdatabase 22 via the navigation ECU 20. The information on this roadshape includes the radius R of curvature of the road per section of theroad (road section) between the current position Pnow and the stopposition Pstop. In other words, the ECU 10 obtains a radius R(px) ofcurvature of the road at the point px.

Based on the radius R(px) of curvature of the road, the ECU 10 computesa lower limit vehicle speed SL(px) at the point px at which the hostvehicle reaches after traveling for the distance x from the currentposition Pnow. As the radius R(px) of curvature is reduced, the curvedroad becomes sharper (a sharper curve). Thus, as the radius R(px) ofcurvature is reduced, visibility worsens (that is, a distance for whicha driver of a vehicle behind can visually recognize the precedingvehicle is short, in other words, timing at which the driver of thevehicle behind recognizes the preceding vehicle tends to be delayed).Based on such a viewpoint, the lower limit vehicle speed SL(px) is setto be increased as the radius R(px) of curvature is reduced. The lowerlimit vehicle speed SL(px) is set to such a speed that, when the hostvehicle travels at a lower speed than the lower limit vehicle speedSL(px), the driver of the vehicle behind has to abruptly brake thevehicle behind immediately after recognizing the host vehicle.

The ECU 10 determines whether the vehicle speed SPD(px) becomes lowerthan the lower limit vehicle speed SL(px) between the current positionPnow and the stop position Pstop. For example, in an example shown inFIG. 2A, the point px at which the vehicle speed SPD(px) becomes lowerthan the lower limit vehicle speed SL(px) does not exist until the stopof the host vehicle. Accordingly, in this case, the ECU 10 immediatelystarts decelerating the host vehicle at the deceleration Dec from a timepoint at which it is determined that the driver is in the drivingincapable abnormal state (that is, an abnormality determination timepoint) tnow. Note that the ECU 10 computes the acceleration of the hostvehicle from a change amount of the vehicle speed SPD per unit time thatis obtained on the basis of a signal from the vehicle speed sensor 16,and transmits a command signal used to make the acceleration correspondto the deceleration Dec (or target acceleration) to the engine ECU 30and the brake ECU 40. This point is the same in the other embodiments.

On the other hand, in an example indicated by a broken line in FIG. 2B,the point px at which the vehicle speed SPD(px) becomes lower than thelower limit vehicle speed SL(px) until the stop of the host vehicleexists. Accordingly, as indicated by a solid line in FIG. 2B, the ECU 10delays a time point at which the host vehicle starts being deceleratedfrom the abnormality determination time point tnow, and decelerates thehost vehicle at the constant deceleration Dec such that the vehiclespeed SPD(px) does not become lower than the lower limit vehicle speedSL(px) in a period from a start of the deceleration of the host vehicleto the stop of the host vehicle. According to this, a situation wherethe host vehicle whose driver is in the driving incapable abnormal state(that is, a deceleration target vehicle) travels at an excessively lowspeed on a sharp curved road with the poor visibility does not occur.Thus, when recognizing the host vehicle, the driver of the vehiclebehind can decelerate or stop without abruptly braking the vehiclebehind.

Furthermore, the first apparatus decelerates the deceleration targetvehicle (the host vehicle) while keeping the constant deceleration. Suchdeceleration with the constant deceleration being kept differs fromdeceleration during vehicle speed automatic control in the normal ACC(will be described below) or the like. Accordingly, occupants includingthe driver of the deceleration target vehicle can receive a sense ofdiscomfort. Thus, if the driver is not in the driving incapable abnormalstate, the driver and passenger, if the passenger exists, can recognizethat the vehicle is forcibly decelerated. In addition, because thedeceleration does not fluctuate, a possibility that the driver of theother vehicle (including the vehicle behind) traveling around thedeceleration target vehicle has to perform a special drive operationsuch as abrupt braking or abrupt steering can be reduced. Note that thiseffect is an effect exerted in a similar manner in another aspect (willbe described below) in which the deceleration target vehicle isdecelerated while keeping the constant deceleration. What has beendescribed so far is the overview of the actuation of the firstapparatus.

(Specific Actuation) Next, a description will be made on specificactuation of the CPU in the ECU 10 according to the first apparatus. TheCPU executes routines shown in flowcharts of FIG. 3 to FIG. 5 every timethe specified time elapses.

-   -   Vehicle Deceleration Start Processing At specified timing, the        CPU starts processing in step 300 in FIG. 3, and the processing        proceeds to step 305. Then, it is determined whether a current        time point is immediately after a value of a flag (a driver        abnormality occurrence flag) Xijo is changed from “0” to “1”,        the flag Xijo indicating that the determination of the driver        being in the driving incapable abnormal state is confirmed. The        value of this flag Xijo is set to “0” in an initial routine,        which is not shown and is executed by the CPU, when an ignition        key switch, which is not shown, is changed from an OFF position        to an ON position. Then, as will be described below, when the        determination that the driver s in the driving incapable        abnormal state is confirmed, the value of this flag Xijo is set        to “1”.

Accordingly, if the driver does not fall in the driving incapableabnormal state after the start of driving of the host vehicle of thistime, the value of the flag Xijo remains “0”. In this case, the CPUdetermines “No” in step 305, and also determines “No” in step 310 inwhich it is determined whether the value of the flag Xijo is “1” Then,the processing directly proceeds to step 395, and this routine isterminated once. Thus, the host vehicle is not forcibly decelerated inthis case.

On the other hand, if it is determined that the driver falls in thedriving incapable abnormal state at the time after the start of drivingof the host vehicle of this time, the value of the flag Xijo is changedfrom “0” to “1”. Immediately after this change, the CPU determines “Yes”in step 305 and sequentially executes the processing from step 315 tostep 345, which will be described below. Then, the processing proceedsto step 350.

Step 315: The CPU stores the vehicle speed SPD that is obtained on thebasis of the signal from the vehicle speed sensor 16 as the currentvehicle speed SPDnow. Step 320: Under assumption that the vehicle isdecelerated from the current vehicle speed SPDnow while keeping theconstant deceleration Dec, the CPU computes the required stop distanceLstop, which is described above, on the basis of the current vehiclespeed SPDnow and the constant deceleration Dec. Step 325: The CPUobtains the current position Pnow from the navigation ECU 20 and storesthe current position Pnow as a deceleration start position Pd. Step 330:Under the assumption that the vehicle is decelerated from the currentvehicle speed SPDnow while keeping the constant deceleration Dec, theCPU computes the vehicle speed SPD(px) at the point px that is a pointin a section from the deceleration start position Pd to a pointseparated therefrom by the required stop distance Lstop and is also apoint at which the host vehicle reaches after traveling for the distancex from the deceleration start position Pd.

Step 335: The CPU identifies a position at which the host vehicle isexpected to be stopped (hereinafter referred to as a “vehicle stopposition”) Pstop from the deceleration start position Pd and therequired stop distance Lstop. Step 340: The CPU obtains the radius R(px)of curvature at the point px in a section from the deceleration startposition Pd to the vehicle stop position Pstop from the map database 22via the navigation ECU 20. In the map database 22, the radius ofcurvature is set per section of the road.

Step 345: The CPU obtains the lower limit vehicle speed SL(px) at thepoint px by applying the radius R(px) of curvature to a lookup tableMapSL(R) shown in a block B1 of FIG. 3. According to the table MapSL(R),a higher value of the lower limit vehicle speed SL(px) is obtained asthe radius R(px) of curvature is reduced. Note that, because the radiusof curvature is set per section of the road in the map database 22, thelower limit vehicle speed SL(px) is also obtained per section of theroad. In other words, the lower limit vehicle speed SL(px) does notchange (is a constant value) in the same section of the road.

Next, the processing proceeds to step 350, and the CPU determineswhether the point px at which the vehicle speed SPD(px) becomes lowerthan the lower limit vehicle speed SL(px) exists. If the point px atwhich the vehicle speed SPD(px) becomes lower than the lower limitvehicle speed SL(px) does not exist (see FIG. 2A), the CPU determines“No” in step 350, the processing proceeds to step 355, and the CPUdetermines whether the current position Pnow of the host vehicle matchesthe deceleration start position Pd. In this case, the current positionPnow matches the deceleration start position Pd due to the processing inabove step 325. Thus, the CPU determines “Yes” in step 355, theprocessing proceeds to step 360, and the CPU starts decelerating thehost vehicle at the constant deceleration Dec. Note that, when the valueof the flag Xijo is “1”, the CPU automatically executes theabove-described lane keeping assist control (LKA). This point is thesame in the other embodiments.

If the CPU executes the processing in step 305 again in this state, theCPU determines “No” in step 305, the processing proceeds to step 310,and the CPU determines “Yes” in step 310. Then, the processing proceedsto step 365, and the CPU determines whether it is a time point beforethe host vehicle starts being decelerated at the constant decelerationDec (before deceleration start). At this time point, the host vehicle isdecelerated. Thus, the CPU determines “No” in step 365, the processingdirectly proceeds to step 395, and this routine is terminated once.

On the other hand, if the point px at which the vehicle speed SPD(px)becomes lower than the lower limit vehicle speed SL(px) exists at a timepoint at which the CPU executes the processing in step 350 (see thebroken line in FIG. 2B), the CPU determines “Yes” in step 350, theprocessing proceeds to step 375, and the CPU sets the deceleration startposition Pd at a position at which the vehicle advances by a distance Z.Thereafter, the CPU repeats the processing from step 330 to step 350.Then, if it is determined in step 350 that the point px at which thevehicle speed SPD(px) becomes lower than the lower limit vehicle speedSL(px) still exists, the CPU sets the deceleration start position Pd ata position at which the vehicle further advances by the distance Z inthe processing in step 375 and repeats the processing from step 330 tostep 350. If the CPU determines that the point px at which the vehiclespeed SPD(px) becomes lower than the lower limit vehicle speed SL(px) nolonger exists after such processing, the processing proceeds from step350 to step 355.

At this time point, the current position Pnow does not match thedeceleration start position Pd. Thus, the CPU determines “No” in step355, the processing directly proceeds to step 395, and this routine isterminated once. Thereafter, when the processing proceeds to step 305again, the CPU determines “No” in step 305, determines “Yes” infollowing step 310, and further determines “Yes” in following step 365.Then, the processing proceeds to step 370. In step 370, the CPU makesthe host vehicle travel at a constant speed so as to keep the vehiclespeed at the time point. Thereafter, the processing proceeds to step355. Accordingly, at the time point at which the current position Pnowof the host vehicle matches the deceleration start position Pd, the CPUdetermines “Yes” in step 355, the processing proceeds to step 360, andthe CPU starts decelerating the host vehicle.

-   -   Vehicle Deceleration Termination Processing At further specified        timing, the CPU starts processing from step 400 in FIG. 4, the        processing proceeds to step 410, and the CPU determines whether        the value of the flag Xijo is “1”. If the value of the flag Xijo        is not “1” (if “0”), the CPU determines “No” in step 410, the        processing directly proceeds to step 495, and this routine is        terminated once.

On the other hand, if the value of the flag Xijo is “1”, the CPUdetermines “Yes” in step 410, the processing proceeds to step 420, andthe CPU determines whether the vehicle speed SPD of the host vehicle is“0” (that is, whether the host vehicle is stopped). If the vehicle speedSPD is not “0”, the CPU determines “No” in step 420, the processingdirectly proceeds to step 495, and this routine is terminated once.

On the other hand, if the vehicle speed SPD is “0”, the CPU determines“Yes” in step 420 and sequentially executes processing in step 430 andstep 440, which will be described below. Then, the processing proceedsto step 495, and this routine is terminated once.

Step 430: The CPU stops the deceleration of the host vehicle. Step 440:The CPU adds the parking braking force to the wheels by using the EPBECU 50. That is, the drive assist ECU 10 keeps the host vehicle in thestopped state. Furthermore, the CPU flashes the hazard lamp 71 by usingthe meter ECU 70 and unlocks a door of the vehicle by using a door lockECU, which is not shown.

-   -   Driver Abnormality Determination At specified timing, the CPU        starts processing from step 500 in FIG. 5, the processing        proceeds to step 510, and determines whether the value of the        flag Xijo is “0”. If the value of the driver abnormality        occurrence flag Xijo is not “0” (if “1”), the CPU determines        “No” in step 510, the processing directly proceeds to step 595,        and this routine is terminated once.

On the other hand, if the value of the flag Xijo is “0”, the CPUdetermines “Yes” in step 510, the processing proceeds to step 520, andthe CPU determines whether the vehicle speed SPD is equal to or higherthan the specified vehicle speed (an abnormality determinationpermitting vehicle speed, a forcible deceleration permitting vehiclespeed) SPDth. If the vehicle speed SPD is not equal to or higher thanthe specified vehicle speed SPDth, the CPU determines “No” in step 520,the processing directly proceeds to step 595, and this routine isterminated once. At this time, the CPU may set a value of an abnormalitydetermination timer Tijo, which will be described below, to “0”. Notethat the specified vehicle speed SPDth is set to a higher value than amaximum value of the lower limit vehicle speed.

On the other hand, if the vehicle speed SPD is equal to or higher thanthe specified vehicle speed SPDth, the CPU determines “Yes” in step 520,the processing proceeds to step 530, and the CPU determines whether acurrent time point corresponds to a non-operating drive state (a nodrive operation state). The non-operating drive state is a state wherenone of the parameters, each of which has a combination of one or moreof “the accelerator pedal operation amount AP, the brake pedal operationamount BP, the steering torque Tra, and the signal level of the stoplamp switch 13”, is changed by the driver. In this example, the CPUregards the state where none of “the accelerator pedal operation amountAP, the brake pedal operation amount BP, and the steering torque Tra” ischanged as the non-operating drive state.

If the current time point does not correspond to the non-operating drivestate, the CPU determines “No” in step 530, the processing proceeds tostep 535, and the CPU sets the value of the abnormality determinationtimer Tijo to “0”. Thereafter, the processing directly proceeds to step595, and this routine is terminated once.

On the other hand, if the current time point corresponds to thenon-operating drive state, the CPU determines “Yes” in step 530, theprocessing proceeds to step 540, and the CPU increases the value of theabnormality determination timer Tijo by “1”. Accordingly, the value ofthe abnormality determination timer Tijo represents duration of thenon-operating drive state.

Next, the processing proceeds to step 550, and the CPU determineswhether the value of the abnormality determination timer Tijo is equalto or longer than a warning start threshold time Tkeikoku. If the valueof the abnormality determination timer Tijo is shorter than the warningstart threshold time Tkeikoku, the CPU determines “No” in step 550, theprocessing directly proceeds to step 595, and this routine is terminatedonce.

On the other hand, if the value of the abnormality determination timerTijo is equal to or longer than the warning start threshold timeTkeikoku, the CPU determines “Yes” in step 550, and the processingproceeds to step 560. The CPU causes the buzzer 81 to generate warningsound, flashes the “warning lamp” on the indicator 82, and displays thewarning message to urge an operation of any of “the accelerator pedal 11a, the brake pedal 12 a, and the steering wheel SW”.

Next, the processing proceeds to step 570, and the CPU determineswhether the value of the abnormality determination timer Tijo is equalto or longer than a driver abnormality determination threshold timeTijoth. The driver abnormality determination threshold time Tijoth isset as a longer time than the warning start threshold time Tkeikoku. Ifthe value of the abnormality determination timer Tijo is shorter thanthe driver abnormality determination threshold time Tijoth, the CPUdetermines “No” in step 570, the processing directly proceeds to step595, and this routine is terminated once.

On the other hand, if the value of the abnormality determination timerTijo is equal to or longer than the driver abnormality determinationthreshold time Tijoth, the CPU determines “Yes” in step 570, the processproceeding to step 580, and the CPU sets the value of the driverabnormality occurrence flag Xijo to “1”. Next, the processing proceedsto step 590, and the CPU prohibits acceleration (including thedeceleration) of the vehicle based on a change in the accelerator pedaloperation amount AP even when the accelerator pedal operation amount APis changed. That is, the CPU prohibits acceleration override. Then, theprocessing proceeds to step 595, and this routine is terminated once.Just as described, when the non-operating drive state continues for thewarning start threshold time Tkeikoku or longer, the warning to urge thedriver to perform the drive operation is issued. Then, when thenon-operating drive state continues for the driver abnormalitydetermination threshold time Tijoth or longer, such a determination thatthe driver is in the driving incapable abnormal state is confirmed, andthe value of the flag Xijo is set to “1”.

As it has been described so far, the first apparatus decelerates thedeceleration target vehicle while controlling the vehicle speed of thedeceleration target vehicle such that the vehicle speed of thedeceleration target vehicle from the abnormality determination timepoint to the time point at which the deceleration target vehicle isstopped does not become lower than the lower limit vehicle speed, whichis set in accordance with the radius of curvature indicative of the roadshape on which the deceleration target vehicle travels (the road shapeon which the deceleration target vehicle travels and the road shape thatinfluences the timing at which the driver of the vehicle behind thedeceleration target vehicle recognizes the deceleration target vehicle).Furthermore, the first apparatus sets the lower limit vehicle speed tothe higher value as the radius of curvature is reduced.

In addition, the first apparatus determines a deceleration start pointsuch that the vehicle speed until the stop of the deceleration targetvehicle does not fall below the lower limit vehicle speed, which is setper section of the road, even when the deceleration target vehicle isdecelerated at the constant deceleration at the abnormalitydetermination time point onward.

Accordingly, when the deceleration target vehicle travels on the curvedroad with the poor visibility, the vehicle speed of the decelerationtarget vehicle is not excessively reduced. Thus, even when the timing atwhich the driver of the vehicle behind recognizes the decelerationtarget vehicle is delayed, the vehicle behind can be decelerated withoutabruptly braking the vehicle behind.

Second Embodiment

Next, a description will be made on a vehicle travel control apparatus(hereinafter may be referred to as a “second apparatus”) according to asecond embodiment of the disclosure. Similar to the first apparatus,when determining that the driver is in the driving incapable abnormalstate, the second apparatus determines whether the point px at which thevehicle speed SPD(px) becomes lower than the lower limit vehicle speedSL(px) exists from the time at which the host vehicle starts beingdecelerated at the constant deceleration Dec to the time at which thehost vehicle is stopped. Then, in the case where the point px, at whichthe vehicle speed SPD(px) becomes lower than the lower limit vehiclespeed SL(px), exists as indicated by a broken line in FIG. 6, the secondapparatus reduces a magnitude of the deceleration at the time ofdecelerating the host vehicle as indicated by a solid line in FIG. 6. Inthis way, the second apparatus decelerates the host vehicle at thereduced deceleration such that the vehicle speed SPD(px) does not becomelower than the lower limit vehicle speed SL(px) until the stop of thehost vehicle. According to this, the driver of the vehicle behind canalso decelerate or stop the vehicle behind without abruptly braking thevehicle behind when recognizing the host vehicle. What has beendescribed so far is the overview of actuation of the second apparatus.

(Specific Actuation) Next, a description will be made on specificactuation of the CPU in the ECU 10 according to the second apparatus.The CPU executes the routines shown in the flowcharts of FIG. 7 whichreplaces FIG. 3, FIG. 4, and FIG. 5 every time a specified time elapses.Because the flowcharts of FIG. 4 and FIG. 5 have already been described,a description will hereinafter be made on actuation (vehicledeceleration start processing) based on the flowchart of FIG. 7.

At the specified timing, the CPU starts processing from step 700 in FIG.7, the processing proceeds to step 705, and the CPU determines whether acurrent time point is immediately after the value of the driverabnormality occurrence flag Xijo is changed from “0” to “1”. If thedriver does not fall in the driving incapable abnormal state after thestart of driving of the host vehicle of this time, the value of the flagXijo is “0”. In this case, the CPU determines “No” in step 705, theprocessing directly proceeds to step 795, and this routine is terminatedonce. Thus, in this case, the host vehicle is not forcibly decelerated.

On the other hand, if it is determined that the driver falls in thedriving incapable abnormal state after the start of driving of the hostvehicle of this time, the value of the flag Xijo is changed from “0” to“1”. In this case, the CPU determines “Yes” in step 705 and sequentiallyexecutes processing from step 710 to step 740, which will be describedbelow. Then, the processing proceeds to step 745.

Step 710: The CPU stores the vehicle speed SPD that is obtained on thebasis of the signal from the vehicle speed sensor 16 as the currentvehicle speed SPDnow. Step 715: The CPU stores (sets) an initial valueDinitial as the deceleration Dec. Step 720: Under the assumption thatthe vehicle is decelerated from the current vehicle speed SPDnow whilekeeping the constant deceleration Dec, the CPU computes the requiredstop distance Lstop, which is described above, on the basis of thecurrent vehicle speed SPDnow and the constant deceleration Dec. Step725: The CPU obtains the current position Pnow of the host vehicle fromthe navigation ECU 20. Then, under the assumption that the host vehicleis decelerated from the current vehicle speed SPDnow while keeping theconstant deceleration Dec, the CPU computes the vehicle speed SPD(px) atthe point px that is a point in a section from the current position Pnowto a point separated therefrom by the required stop distance Lstop andis also a point at which the host vehicle reaches after traveling fromthe current position Pnow for the distance x.

Step 730: The CPU identifies the vehicle stop position Pstop of the hostvehicle from the current position Pnow of the host vehicle and therequired stop distance Lstop. Step 735: The CPU obtains the radius R(px)of curvature at the point px in a section from the current position Pnowof the host vehicle to the vehicle stop position Pstop from the mapdatabase 22 via the navigation ECU 20. As described above, in the mapdatabase 22, the radius of curvature is set per section of the road.Step 740: The CPU obtains the lower limit vehicle speed SL(px) at thepoint px by applying the radius R(px) of curvature to the lookup tableMapSL(R) shown in a block B1 of FIG. 7. According to the table MapSL(R),the higher value of the lower limit vehicle speed SL(px) is obtained asthe radius R(px) of curvature is reduced. Note that, as described above,the lower limit vehicle speed SL(px) is obtained per section of theroad.

Next, the processing proceeds to step 745, and the CPU determineswhether the point px at which the vehicle speed SPD(px) becomes lowerthan the lower limit vehicle speed SL(px) exists. If the point px atwhich the vehicle speed SPD(px) becomes lower than the lower limitvehicle speed SL(px) does not exist (see FIG. 2A), the CPU determines“No” in step 745, the processing proceeds to step 750, and the CPUstarts decelerating the host vehicle at the constant deceleration Dec.

On the other hand, if the point px at which the vehicle speed SPD(px)becomes lower than the lower limit vehicle speed SL(px) exists (see thebroken line in FIG. 6), the CPU determines “Yes” in step 745, theprocessing proceeds to step 755, and the CPU reduces the magnitude ofthe deceleration Dec by a positive value β. Thereafter, the CPU repeatsthe processing from step 720 to step 745. As a result of this, if thepoint px at which the vehicle speed SPD(px) becomes lower than the lowerlimit vehicle speed SL(px) no longer exists, the processing proceedsfrom step 745 to step 750, and the CPU starts decelerating the hostvehicle at the constant deceleration Dec whose magnitude is reduced bythe positive value β. Note that step 755 is repeatedly executed unlessit is determined “No” in step 745. Thus, the magnitude of thedeceleration Dec is gradually reduced.

As it has been described so far, similar to the first apparatus, thesecond apparatus decelerates the deceleration target vehicle whilecontrolling the vehicle speed of the deceleration target vehicle suchthat the vehicle speed of the deceleration target vehicle from theabnormality determination time point to the time point at which thedeceleration target vehicle is stopped does not become lower than thelower limit vehicle speed, which is set in accordance with the radius ofcurvature indicative of the road shape on which the deceleration targetvehicle travels. Furthermore, the second apparatus sets the lower limitvehicle speed to the higher value as the radius of curvature is reduced.

In addition, the second apparatus determines the deceleration at whichthe vehicle speed until the stop of the deceleration target vehicle doesnot fall below the lower limit vehicle speed, which is set per sectionof the road. Then, the second apparatus decelerates the decelerationtarget vehicle while keeping the deceleration.

Accordingly, when the deceleration target vehicle travels on the curvedroad with the poor visibility, the vehicle speed of the decelerationtarget vehicle is not excessively reduced. Thus, even when the timing atwhich the driver of the vehicle behind recognizes the decelerationtarget vehicle is delayed, the vehicle behind can be decelerated withoutabruptly braking the vehicle behind.

Third Embodiment

Next, a description will be made on a vehicle travel control apparatus(hereinafter may be referred to as a “third apparatus”) according to athird embodiment of the disclosure. When determining that the driver isin the driving incapable abnormal state, the third apparatus obtainsinformation on a road shape between the current position Pnow and atentative stop position Ptstop that is ahead of the current positionPnow by a sufficient distance to stop the vehicle (hereinafter referredto as a “maximum predicted stop distance”) from the map database 22 viathe navigation ECU 20. This information on the road shape also includesthe radius R of curvature per section of the road between the currentposition Pnow and the tentative stop position Ptstop. In other words,the ECU 10 obtains the radius R(px) of curvature of the road at thepoint px. Next, the third apparatus computes the lower limit vehiclespeed SL(px) at the point px on the basis of the radius R(px) ofcurvature.

Then, the third apparatus computes a vehicle speed SL(px) at the pointpx in a case where the host vehicle is decelerated at the constantdeceleration Dec. In the case where it is predicted that the vehiclespeed SL(px) becomes lower than the lower limit vehicle speed SL(px),the deceleration of the host vehicle is temporarily stopped to keep thevehicle speed (see a solid line in FIG. 8) in a period in which thevehicle speed SL(px) becomes lower than the lower limit vehicle speedSL(px) (see a broken line in FIG. 8 and a period from time t1 to timet2). Thereafter, when the vehicle speed SL(px) is brought into a stateof being equal to or higher than the lower limit vehicle speed SL(px),the third apparatus decelerates the host vehicle at the constantdeceleration Dec again. The third apparatus obtains a target vehiclespeed SPDtgt, at which the host vehicle is decelerated just asdescribed, through calculation at the abnormality determination timepoint. Then, at the abnormality determination time point onward, thethird apparatus gradually decelerates the host vehicle such that thevehicle speed SPD of the host vehicle matches the target vehicle speedSPDtgt. According to this, the driver of the vehicle behind can alsodecelerate or stop the vehicle behind without abruptly braking thevehicle behind when recognizing the host vehicle. What has beendescribed so far is the overview of actuation of the third apparatus.

(Specific Actuation) Next, a description will be made on specificactuation of the CPU in the ECU 10 according to the third apparatus. TheCPU executes the routines shown in the flowcharts of FIG. 9 whichreplaces FIG. 3, FIG. 4, and FIG. 5 every time a specified time elapses.Because the flowcharts of FIG. 4 and FIG. 5 have already been described,a description will hereinafter be made on actuation (vehicledeceleration processing) based on the flowchart of FIG. 9.

At specified timing, the CPU starts the processing from step 900 in FIG.9, the processing proceeds to step 910, and the CPU determines whether acurrent time point is immediately after the value of the driverabnormality occurrence flag Xijo is changed from “0” to “1”. If thedriver does not fall in the driving incapable abnormal state after thestart of driving of the host vehicle of this time, the value of the flagXijo is “0”. In this case, the CPU determines “No” in step 910, theprocessing directly proceeds to step 995, and this routine is terminatedonce. Thus, in this case, the host vehicle is not forcibly decelerated.

On the other hand, if a time point at which the CPU executes theprocessing in step 910 is immediately after the value of the flag Xijois changed from “0” to “1”, the CPU determines “Yes” in step 910 andsequentially executes processing from step 920 to step 960, which willbe described below. Then, the processing proceeds to step 995, and thisroutine is terminated once.

Step 920: The CPU stores the vehicle speed SPD that is obtained on thebasis of the signal from the vehicle speed sensor 16 as the currentvehicle speed SPDnow. Step 930: The CPU obtains the radius R(px) ofcurvature at the point px in a section from the current position Pnow ofthe host vehicle to the above-described tentative stop position Ptstopfrom the map database 22 via the navigation ECU 20. As described above,in the map database 22, the radius of curvature is set per section ofthe road.

Step 940: The CPU obtains the lower limit vehicle speed SL(px) at thepoint px by applying the radius R(px) of curvature to the lookup tableMapSL(R) shown in a block B1 of FIG. 9. According to the table MapSL(R),the higher value of the lower limit vehicle speed SL(px) is obtained asthe radius R(px) of curvature is reduced. As described above, the lowerlimit vehicle speed SL(px) is obtained per section of the road. Step950: Under assumption that the vehicle is decelerated from the currentvehicle speed SPDnow at the constant deceleration Dec, the CPUdetermines the target vehicle speed SPDtgt by the above-described method(see a time chart in a block Ex of FIG. 9).

Step 960: The CPU executes required processing so as to gradually reducethe vehicle speed SPD of the host vehicle in accordance with the targetvehicle speed SPDtgt, which is determined in step 950. As a result ofthis, in an example shown in the time chart in the block Ex of FIG. 9,the host vehicle travels at the constant speed from time t1 to time t2;however, the host vehicle is decelerated while keeping the constantdeceleration Dec in the other period.

As it has been described so far, the third apparatus decelerates thedeceleration target vehicle at the constant deceleration at theabnormality determination time point onward. In a period from theabnormality determination time point to the time point at which thedeceleration target vehicle is stopped, the deceleration of thedeceleration target vehicle is temporarily interrupted, and the vehiclespeed thereof is kept (the vehicle travels at the constant speed) in aperiod in which the vehicle speed of the deceleration target vehicle isexpected to become lower than the lower limit vehicle speed, which isset per section of the road. The host vehicle is decelerated at theconstant deceleration in a period in which the host vehicle does nottravel at the constant speed.

Thus, it is possible to prevent the vehicle speed of the decelerationtarget vehicle from falling below the lower limit vehicle speed. It isalso possible to continue the deceleration of the deceleration targetvehicle when the vehicle speed of the deceleration target vehicle ishigher than the lower limit vehicle speed. As a result, the vehiclespeed of the deceleration target vehicle can be reduced to be as low aspossible while the vehicle speed of the deceleration target vehicle isprevented from falling below the lower limit vehicle speed.

Fourth Embodiment

Next, a description will be made on a vehicle travel control apparatus(hereinafter may be referred to as a “fourth apparatus”) according to afourth embodiment of the disclosure. The fourth apparatus calculates theradius of curvature of the road, on which the host vehicle travels, onthe basis of the image data (the road image data) obtained by the cameradevice 17 b, and determines the lower limit vehicle speed on the basisof the radius of curvature.

By the way, a radius of curvature of a road on which the host vehiclewill travel in the future can be obtained (obtained in advance) on thebasis of the road image data obtained by the camera device 17 b when theroad is located in front of the host vehicle and is located within aspecified distance L from the host vehicle. Accordingly, the fourthapparatus changes a travel state of the host vehicle on the basis of afuture vehicle speed of the host vehicle and the radius of curvature ofthe road on which the host vehicle will travel in the future.

A description will hereinafter be made on characteristic actuation ofthe fourth apparatus on the basis of examples shown in FIG. 10A to FIG.10D and FIG. 11A to FIG. 11D. Note that, in FIG. 10A to FIG. 10D andFIG. 11A to FIG. 11D, solid lines indicate “the radius of curvature, thevehicle speed, and the lower limit vehicle speed” up to the current timepoint, broken lines indicate “the radius of curvature and the lowerlimit vehicle speed of the road on which the host vehicle will travel ata future time point” obtained by using the camera device 17 b, andone-dot chain lines indicate the future vehicle speed (a predictedvehicle speed) of the host vehicle. FIG. 10A to FIG. 10D are timecharts, and the actuation of the fourth apparatus is changed from FIG.10A to FIG. 10B, FIG. 10C, and FIG. 10D along with a lapse of time.Similarly, FIG. 11A to FIG. 11D are time charts, and the actuation ofthe fourth apparatus is changed from FIG. 11A to FIG. 11B, FIG. 11C, andFIG. 11D along with the lapse of the time.

Example 1

As indicated by the broken line in FIG. 10A, in the case where a futureradius of curvature that can be obtained at the abnormalitydetermination time point is relatively large, the lower limit vehiclespeed remains as the low vehicle speed. Accordingly, as indicated by theone-dot chain line, even when the host vehicle is decelerated at theconstant deceleration from the abnormality determination time point, thefuture vehicle speed does not become lower than the lower limit vehiclespeed. Thus, in this case, the fourth apparatus starts decelerating thehost vehicle at the constant deceleration from the abnormalitydetermination time point.

Thereafter, as shown in FIG. 10B, when the current time point becomes atime point t1, it is assumed that an abrupt reduction in the radius ofcurvature at a certain time point t3 in the future and an abruptincrease in the lower limit vehicle speed as a result are predicted. Inthis case, the vehicle speed of the host vehicle at the time point t1 ishigher than the lower limit vehicle speed at the time point t3. However,in the case where the host vehicle keeps being decelerated at theconstant deceleration, it is predicted that the vehicle speed becomeslower than the lower limit vehicle speed at the time point t3.Accordingly, as shown in FIG. 10C, the fourth apparatus temporarilystops the deceleration at the time point t1, at which such a predictionis made, makes the host vehicle travel at the constant speed, andthereby keeps the vehicle speed.

Thereafter, the fourth apparatus predicts that the vehicle speed doesnot become lower than the lower limit vehicle speed in the future evenwhen decelerating the host vehicle at the constant deceleration (see atime point t2 in FIG. 10C). At this time, the fourth apparatus startsdecelerating the host vehicle again at the constant deceleration. As aresult, as shown in FIG. 10D, the vehicle speed is reduced withoutfalling below the lower limit vehicle speed and eventually becomes “0”.

Example 2

As indicated by the broken line in FIG. 11A, in the case where thefuture radius of curvature that can be obtained at the abnormalitydetermination time point is relatively large, the lower limit vehiclespeed remains as the low vehicle speed. Accordingly, as indicated by theone-dot chain line, even when the host vehicle is decelerated at theconstant deceleration from the abnormality determination time point, thefuture vehicle speed does not become lower than the lower limit vehiclespeed. Thus, in this case, the fourth apparatus starts decelerating thehost vehicle at the constant deceleration from the abnormalitydetermination time point.

Thereafter, as shown in FIG. 11B, when the current time point becomesthe time point t1, it is assumed that the abrupt reduction in the radiusof curvature at the certain time point t3 in the future and the abruptincrease in the lower limit vehicle speed as a result are predicted. Inthis case, the vehicle speed of the host vehicle at the time point t1 isalready lower than the lower limit vehicle speed at the time point t3.Thus, in the case where the host vehicle keeps being decelerated at theconstant deceleration, it is predicted that the vehicle speed naturallybecomes lower than the lower limit vehicle speed at the time point t3.Accordingly, as shown in FIG. 11C, the fourth apparatus temporarilystops the deceleration at the time point t1, at which such a predictionis made, and accelerates the host vehicle at specified acceleration.This specified acceleration is acceleration that is calculated such thatthe vehicle speed of the host vehicle reaches a higher vehicle speedthan the lower limit vehicle speed that corresponds to the radius ofcurvature corresponding to the time point t3 (a value that is obtainedby adding a constant vehicle speed to the lower limit vehicle speed)before the host vehicle reaches a point with the radius of curvature.Then, when the vehicle speed of the host vehicle reaches the lower limitvehicle speed at the point with the radius of curvature corresponding tothe time point t3, the fourth apparatus makes the host vehicle travel atthe constant speed (see the time point t2).

Thereafter, the fourth apparatus predicts that the vehicle speed doesnot become lower than the lower limit vehicle speed in the future evenwhen decelerating the host vehicle at the constant deceleration (see atime point t4 in FIG. 11C and FIG. 11D). At this time, the fourthapparatus starts decelerating the host vehicle again at the constantdeceleration. As a result, as shown in FIG. 11D, the vehicle speed isreduced without falling below the lower limit vehicle speed andeventually becomes “0”.

(Specific Actuation) Next, a description will be made on specificactuation of the CPU in the ECU 10 according to the fourth apparatus.The CPU executes the routines shown in the flowcharts of FIG. 12 whichreplaces FIG. 3, FIG. 4, and FIG. 5 every time a specified time elapses.Because the flowcharts of FIG. 4 and FIG. 5 have already been described,a description will hereinafter be made on actuation (vehicledeceleration processing) based on the flowchart of FIG. 12.

At specified timing, the CPU starts the processing from step 1200 inFIG. 12, the processing proceeds to step 1205, and the CPU determineswhether the value of the driver abnormality occurrence flag Xijo is “1”.If the driver does not fall in the driving incapable abnormal stateafter the start of driving of the host vehicle of this time, the valueof the flag Xijo is “0”. In this case, the CPU determines “No” in step1205, the processing directly proceeds to step 1295, and this routine isterminated once. Thus, in this case, the host vehicle is not forciblydecelerated.

On the other hand, if the value of the driver abnormality occurrenceflag Xijo is “1” at a time point at which the CPU executes theprocessing in step 1205, the CPU determines “Yes” in step 1205, theprocessing proceeds to step 1210, and the CPU determines whether thevehicle speed SPD is higher than “0”. If the vehicle speed SPD is “0”,the CPU determines “No” in step 1210. Then, the processing directlyproceeds to step 1295, and this routine is terminated once.

On the other hand, if the vehicle speed SPD is higher than “0”, the CPUdetermines “Yes” in step 1210, the processing proceeds to step 1215, andthe CPU determines whether a value of an acceleration flag Xkasoku is“0”. When the value of the acceleration flag Xkasoku is “1”, theacceleration flag Xkasoku indicates that the host vehicle is acceleratedat the abnormality determination time point onward. The accelerationflag Xkasoku is set to “0” in the above-described initial routine is setto “1” in step 1260 which will be described below, and is further set to“0” in step 1270 which will be described below.

Here, if the current time point is immediately after the abnormalitydetermination time point, the value of the acceleration flag Xkasoku is“0”. Thus, the CPU determines “Yes” in step 1215 and sequentiallyexecutes processing from step 1220 to step 1225, which will be describedbelow. Then, the processing proceeds to step 1230.

Step 1220: Based on the road image data obtained by the camera device 17b, the CPU calculates and obtains a radius R(x) of curvature of the roadahead of the road on which the host vehicle travels at the current timepoint (a radius of curvature of a position ahead of the current positionof the host vehicle by a specified distance x). Note that a maximumvalue L of the specified distance x is a maximum distance with which theradius of curvature can be computed on the basis of the road image dataobtained by the camera device 17 b. Step 1225: The CPU determines alower limit vehicle speed SL(x) that corresponds to the radius R(x) ofcurvature of the position ahead by the specified distance x by applyingthe radius R(x) of curvature to the lookup table MapSL(R) shown in ablock B3 of FIG. 12. The distance x is equal to or longer than “0” andis equal to or shorter than “L” According to this table MapSL(R), thelower limit vehicle speed SL(x) is calculated to be increased as theradius R(x) of curvature is reduced.

Next, the processing proceeds to step 1230, and the CPU determineswhether the vehicle speed SPD at the current time point is lower than a“lower limit vehicle speed SL(L) at the position ahead of the currentposition of the host vehicle by the specified distance L”. The specifieddistance L is the maximum value of the above-described specifieddistance x. If the vehicle speed SPD at the current time point is equalto or higher than the lower limit vehicle speed SL(L), the CPUdetermines “No” in step 1230, and the processing proceeds to step 1235.Then, the CPU determines whether “vehicle speed SPD(x) at the positionahead of the current position of the host vehicle by the specifieddistance x (x is the distance that is equal to or longer than 0 and isequal to or shorter than the specified distance L)” becomes lower thanthe lower limit vehicle speed SL(x) in the case where the host vehicleis decelerated at the constant deceleration Dec. That is, the CPUdetermines whether a situation shown in FIG. 10B occurs.

If a determination condition is not established in step 1235, the CPUdetermines “No” in step 1235, the processing proceeds to step 1240, andthe CPU decelerates the host vehicle at the constant deceleration Dec.On the other hand, if the determination condition of step 1235 isestablished, the CPU determines “Yes” in step 1235, the processingproceeds to step 1245, and the CPU makes the host vehicle travel at theconstant speed so as to keep the current vehicle speed (see the timepoint t1 in FIG. 10C).

Thereafter, if such a state continues, the CPU determines “Yes” in allsteps from step 1205 to step 1215, and the processing proceeds to step1230 via step 1220 and step 1225. At this time point, the vehicle speedis kept to be constant. Accordingly, unless a road with a smaller radiusof curvature appears, a situation where the determination condition ofstep 1230 is not established continues, and thus the CPU keepsdetermining “No” in step 1230. The CPU thereby repeats the determinationin step 1235. Thus, at the time point t2 in FIG. 10C, the CPU determines“No” in step 1235, and the processing proceeds to step 1240. Then, theCPU starts decelerating the host vehicle again at the constantdeceleration Dec.

By the way, at a time point at which the CPU executes the processing instep 1230 like the time point t1 in FIG. 11B, there is a case where thevehicle speed SPD at the current time point becomes lower than the lowerlimit vehicle speed SL(L). In the case where the host vehicle isdecelerated at the constant deceleration Dec at this time, it ispredicted that a vehicle speed SPD(L) at the position ahead of thecurrent position of the host vehicle by the specified distance Lnaturally becomes lower than the lower limit vehicle speed SL(L).Accordingly, in this case, the CPU determines “Yes” in step 1230 andsequentially executes processing from step 1250 to step 1260, which willbe described below. Then, the processing proceeds to step 1295, and thisroutine is terminated once.

Step 1250: The CPU stores the lower limit vehicle speed SL(L) that isused as the determination condition of step 1230 (that is, SL(L) of thelower limit vehicle speed SL(x) obtained in last step 1225) as areference target vehicle speed SLm. Step 1255: Based on the vehiclespeed SPD and the specified distance L at the time point, the CPUcomputes constant acceleration Ac at which the vehicle speed SPD(L) atthe time when the host vehicle travels for the specified distance L cancorrespond to a “value (SLm+ΔS) that is obtained by adding a specifiedpositive vehicle speed (margin) ΔS to the reference target vehicle speedSLm” and accelerates the host vehicle at the constant acceleration Ac.Step 1260: The CPU sets the value of the acceleration flag Xkasoku to“1”.

If the CPU starts the processing from step 1200 again in this state, theCPU determines “Yes” in step 1205 and step 1210 and determines “No” infollowing step 1215, and the processing proceeds to step 1265. The CPUdetermines in step 1265 whether the vehicle speed SPD at the time pointis higher than the reference target vehicle speed SLm. If the vehiclespeed SPD at the time point is equal to or lower than the referencetarget vehicle speed SLm, the CPU determines “No” in step 1265. Then,the processing directly proceeds to step 1295, and this routine isterminated once. As a result of this, the host vehicle keeps beingaccelerated at the constant acceleration Ac.

As a result of the acceleration of the host vehicle, as shown at thetime point t2 in FIG. 11C, if the vehicle speed SPD at the time pointbecomes higher than the reference target vehicle speed SLm, the CPUdetermines “Yes” in step 1265. Then, the processing proceeds to step1270, and the CPU sets the value of the acceleration flag Xkasoku to“0”.

Accordingly, when executing this routine next time, the CPU determines“Yes” in step 1215 and determines “No” in step 1230. Then, theprocessing proceeds to step 1235. Thus, the CPU keeps the constanttravel by the processing in step 1245 until the CPU determines that thevehicle speed SPD(x) does not become lower than the lower limit vehiclespeed SL(x) in the case where the host vehicle is decelerated at theconstant deceleration Dec. If the CPU determines that the vehicle speedSPD(x) does not become lower than the lower limit vehicle speed SL(x) inthe case where the host vehicle is decelerated at the constantdeceleration Dec, the deceleration by the processing in step 1240 isresumed.

As it has been described so far, based on the image data obtained by thecamera device 17 b, the fourth apparatus obtains the radius of curvature(or curvature=1/the radius of curvature) of the road at the particularpoint that is ahead of the position of the vehicle at the current timepoint by the specified distance L.

Then, in the case where it is predicted that the vehicle speed at thetime when the deceleration target vehicle reaches the particular pointbecomes lower than the lower limit vehicle speed, which is set on thebasis of the radius of curvature (or the curvature) of the particularpoint, (including the case where the vehicle speed at the current timepoint is lower than the lower limit vehicle speed at the particularpoint) when the deceleration target vehicle keeps being decelerated, thefourth apparatus makes the deceleration target vehicle travel at theconstant speed or accelerates the deceleration target vehicle, so as tokeep the vehicle speed of the deceleration target vehicle at the time ofreaching the particular point to be equal to or higher than the lowerlimit vehicle speed.

Thus, even when the information of the map database cannot be used, evenwhen the information of the map database is old information, or thelike, the fourth apparatus can gradually reduce the vehicle speed of thedeceleration target vehicle while preventing the vehicle speed of thedeceleration target vehicle from significantly falling below the lowerlimit vehicle speed.

Fifth Embodiment

Next, a description will be made on a vehicle travel control apparatus(hereinafter may be referred to as a “fifth apparatus”) according to afifth embodiment of the disclosure. When determining that the driver isin the driving incapable abnormal state, the fifth apparatus deceleratesthe host vehicle at the constant deceleration Dec, calculates a radiusRnow of curvature of the road at the position at which the host vehicletravels at the current time point on the basis of the road image dataobtained by the camera device 17 b, and determines a lower limit vehiclespeed SLnow on the basis of the radius Rnow of curvature.

Then, in the case where the vehicle speed SPD becomes equal to or lowerthan the lower limit vehicle speed SLnow by the time the host vehicle isstopped, the fifth apparatus temporarily stops the deceleration andkeeps or increases the vehicle speed. Thereafter, when the vehicle speedSPD is brought into a state of being higher than the lower limit vehiclespeed SLnow, the fifth apparatus decelerates the host vehicle again atthe constant deceleration Dec. According to this, the vehicle speed ofthe host vehicle does not significantly fall below the lower limitvehicle speed, either. Thus, when recognizing the host vehicle, thedriver of the vehicle behind can decelerate or stop without abruptlybraking the vehicle behind. What has been described so far is theoverview of actuation of the fifth apparatus.

(Specific Actuation) Next, a description will be made on specificactuation of the CPU in the ECU 10 according to the fifth apparatus. TheCPU executes the routines shown in the flowcharts of FIG. 13 whichreplaces FIG. 3, FIG. 4, and FIG. 5 every time a specified time elapses.Because the flowcharts of FIG. 4 and FIG. 5 have already been described,a description will hereinafter be made on actuation (vehicledeceleration processing) based on the flowchart of FIG. 13.

At specified timing, the CPU starts the processing from step 1300 inFIG. 13, the processing proceeds to step 1310, and the CPU determineswhether the value of the driver abnormality occurrence flag Xijo is “1”.If the value of the flag Xijo is not “1”, the CPU determines “No” instep 1310, the processing directly proceeds to step 1395, and thisroutine is terminated once. Thus, in this case, the host vehicle is notforcibly decelerated.

On the other hand, if the value of the driver abnormality occurrenceflag Xijo is “1” at a time point at which the CPU executes theprocessing in step 1310, the CPU determines “Yes” in step 1310, theprocessing proceeds to step 1320, and the CPU determines whether thevehicle speed SPD is higher than “0”. If the vehicle speed SPD is “0”,the CPU determines “No” in step 1320. Then, the processing directlyproceeds to step 1395, and this routine is terminated once.

On the other hand, if the vehicle speed SPD is higher than “0”, the CPUdetermines “Yes” in step 1320 and sequentially executes processing instep 1330 and step 1340, which will be described below. Then, theprocessing proceeds to step 1350.

Step 1330: Based on the road image data obtained by the camera device 17b, the CPU calculates and obtains the radius Rnow of curvature of theroad on which the host vehicle travels at the current time point. Step1340: The CPU determines the lower limit vehicle speed SLnow at thecurrent time point by applying the radius Rnow of curvature to a lookuptable MapSLnow(Rnow) shown in a block B2 of FIG. 13. According to thistable MapSLnow(Rnow), the lower limit vehicle speed SLnow is computed tobe increased as the radius Rnow of curvature is reduced.

Next, the processing proceeds to step 1350, and the CPU determineswhether the vehicle speed SPD at the current time point is higher thanthe lower limit vehicle speed SLnow at the current time point. If thevehicle speed SPD at the current time point is higher than the lowerlimit vehicle speed SLnow at the current time point, the CPU determines“Yes” in step 1350, the processing proceeds to step 1360, and the CPUdecelerates the host vehicle at the constant deceleration Dec.Thereafter, the processing proceeds to 1395, and this routine isterminated once.

On the other hand, if the vehicle speed SPD at the current time point isequal to or lower than the lower limit vehicle speed SLnow at thecurrent time point, the CPU determines “No” in step 1350, the processingproceeds to step 1370, and the CPU temporarily stops the deceleration atthe constant deceleration Dec. In addition, if the vehicle speed SPD atthe current time point is equal to the lower limit vehicle speed SLnowat the current time point, the CPU makes the host vehicle travel at theconstant speed. If the vehicle speed SPD at the current time point islower than the lower limit vehicle speed SLnow at the current timepoint, the CPU accelerates the host vehicle at constant acceleration Accuntil the vehicle speed SPD of the host vehicle matches the lower limitvehicle speed SLnow. Thereafter, the processing proceeds to step 1395,and this routine is terminated once.

As it has been described so far, based on the image data obtained by thecamera device 17 b, the fifth apparatus obtains information on theradius of curvature of the road at the point on which the decelerationtarget vehicle travels at the “current time point”. Then, the fifthapparatus sets the lower limit vehicle speed to a higher value as theradius of curvature indicated by the information on the radius ofcurvature is reduced. Furthermore, in the case where the vehicle speedof the deceleration target vehicle at the current time point is higherthan the lower limit vehicle speed at the point at which thedeceleration target vehicle travels at the current time point, the fifthapparatus decelerates the deceleration target vehicle. In the case wherethe vehicle speed of the deceleration target vehicle at the current timepoint is equal to the lower limit vehicle speed at the point at whichthe deceleration target vehicle travels at the current time point, thefifth apparatus makes the deceleration target vehicle travel at theconstant speed. In the case where the vehicle speed of the decelerationtarget vehicle at the current time point is lower than the lower limitvehicle speed at the point at which the deceleration target vehicletravels at the current time point, the fifth apparatus accelerates thedeceleration target vehicle or makes the deceleration target vehicletravel at the constant speed.

Accordingly, even when the information of the map database cannot beused, even when the information of the map database is the oldinformation, or the like, the fifth apparatus can gradually reduce thevehicle speed of the deceleration target vehicle while preventing thevehicle speed of the deceleration target vehicle from significantlyfalling below the lower limit vehicle speed.

Modified Example of Fifth Embodiment

Next, a description will be made on a vehicle travel control apparatus(hereinafter may be referred to as a “fifth modified example apparatus”)according to a modified example of the fifth embodiment of thedisclosure. The fifth modified example apparatus differs from the fifthapparatus only in a point that the fifth modified example apparatuscorrects the lower limit vehicle speed SLnow in accordance with whetherthe wall (the roadside wall) exists on the road on which the hostvehicle travels, whether it is in bad weather (rainy or foggy), whetherit is nighttime, and whether height of the host vehicle is low. Thus, adescription will hereinafter be centered on this different point.

(Specific Actuation) A CPU of the drive assist ECU 10 according to thefifth modified example apparatus differs from that according to thefifth apparatus only in a point that step 1340 of FIG. 13 is replacedwith step 1405 to step 1480 shown in FIG. 14.

That is, after the CPU obtains the radius Rnow of curvature in step1330, the processing proceeds to step 1405 in FIG. 14, and the CPUdetermines a reference value of the lower limit vehicle speed SLnow (areference lower limit vehicle speed) SLnowb at the current time point byapplying the radius Rnow of curvature of the road on which the hostvehicle travels at the current time point to a lookup tableMapSLnowb(Rnow) shown in a block B2 a of FIG. 14. This tableMapSLnowb(Rnow) is the same as the table MapSLnow(Rnow). According tothis, the reference lower limit vehicle speed SLnowb is computed to beincreased as the radius Rnow of curvature is reduced.

Next, the processing proceeds to step 1410, and the CPU deter mineswhether the radius Rnow of curvature is equal to or smaller than athreshold Rnowth of radius of curvature. That is, the CPU determineswhether the host vehicle travels on the relatively sharp curved road(the sharp curve) at the current time point. If the radius Rnow ofcurvature is equal to or smaller than the threshold Rnowth of radius ofcurvature, the CPU determines “Yes” in step 1410, the processingproceeds to step 1415, and the CPU determines whether the road on whichthe host vehicle travels at the current time point is a right curvedroad (a right curve) and the roadside wall such as a noise abatementwall is provided on a right side of the road on the basis of the roadimage data. If the road on which the host vehicle travels at the currenttime point is the right curved road (the right curve) and the roadsidewall is provided on the right side of the road, the CPU determines “Yes”in step 1415, the processing proceeds to step 1420, and the CPU sets avalue of a correction coefficient kR to “1+d1”. The value d1 is a valuethat is larger than 0 and smaller than 1 (for example, 0.1). Thereafter,the processing proceeds to step 1435.

On the other hand, if a determination condition of step 1415 is notestablished, the processing proceeds from step 1415 to step 1425, andthe CPU determines whether the road on which the host vehicle travels atthe current time point is a left curved road (a left curve) and theroadside wall such as the noise abatement wall is provided on a leftside of the road on the basis of the road image data. If the road onwhich the host vehicle travels at the current time point is the leftcurved road (the left curve) and the roadside wall is provided on theleft side of the road, the CPU determines “Yes” in step 1425, theprocessing proceeds to step 1427, and the CPU sets a value of acorrection coefficient kL to “1+d2”. The value d2 is a value that islarger than 0 and smaller than 1 (for example, 0.1). Thereafter, theprocessing proceeds to step 1435.

Furthermore, if a determination condition of step 1425 is notestablished, the processing proceeds from step 1425 to step 1430, andthe CPU sets each of the correction coefficient kR and the correctioncoefficient kL to “1”. Thereafter, the processing proceeds to step 1435.Note that, if the radius Rnow of curvature is not equal to or smallerthan the threshold Rnowth of radius of curvature at a time point atwhich the CPU executes the processing in step 1410, the CPU determines“No” in step 1410, and the processing proceeds to step 1430 and nextproceeds to step 1435. Accordingly, also in this case, each of thecorrection coefficient kR and the correction coefficient kL is set to“1”.

When the processing proceeds to step 1435, the CPU determines whether itis rainy or foggy at the current time point. For example, the CPUdetermines whether a windshield wiper, which is not shown, of the hostvehicle is actuated. If the windshield wiper is actuated, the CPUdetermines that the weather at the current time point is rainy.Furthermore, for example, the CPU determines whether a fog lamp, whichis not shown, of the host vehicle is lit. If the fog lamp is lit, theCPU determines it is foggy at the current time point. Note that the CPUmay obtain information on weather (whether it is rainy and foggy, andthe like) of a region where the host vehicle travels from outside (forexample, a weather information providing center) by using acommunication device with the outside, which is not shown, and mayexecute the processing in step 1435 on the basis of the information.

If the determination condition of step 1435 is established, theprocessing proceeds to step 1440, and the CPU sets a value of acorrection coefficient kW to “1+d3”. The value d3 is a value that islarger than 0 and smaller than 1 (for example, 0.1). Thereafter, theprocessing proceeds to step 1450. On the other hand, if thedetermination condition of step 1435 is not established, the processingproceeds to step 1445, and the CPU sets the value of the correctioncoefficient kW to “1” Thereafter, the processing proceeds to step 1450.

When the processing proceeds to step 1450, the CPU determines whether itis the nighttime at the current time point. For example, the CPUdetermines whether a headlight, which is not shown, of the host vehicleis lit. If the headlight is lit, the CPU determines that it is thenighttime at the current time point. Note that the CPU may determinewhether it is the nighttime at the current time point by using anilluminance sensor, which is not shown (for example, see Japanese PatentNo. 4465817).

If a determination condition of step 1450 is established, the processingproceeds to step 1455, and the CPU sets a value of a correctioncoefficient kN to “1+d4”. The value d4 is a value that is larger than 0and smaller than 1 (for example, 0.1). Thereafter, the processingproceeds to step 1465. On the other hand, if the determination conditionof step 1450 is not established, the processing proceeds to step 1460,and the CPU sets the value of the correction coefficient kN to “1”.Thereafter, the processing proceeds to step 1465.

When the processing proceeds to step 1465, the CPU reads “vehicle heightH of the host vehicle” that is stored in the ROM of the ECU 10, anddetermines whether the vehicle height H is equal to or lower than avehicle height threshold Hth. If the vehicle height H is equal to orlower than the vehicle height threshold Hth, the processing proceeds tostep 1470, and the CPU sets a value of a correction coefficient kH to“1+d5”. The value d5 is a value that is larger than 0 and smaller than 1(for example, 0.1). Thereafter, the processing proceeds to step 1480. Onthe other hand, if the vehicle height H is higher than the vehicleheight threshold Hth, the processing proceeds to step 1475, and the CPUsets the value of the correction coefficient kH to “1”. Thereafter, theprocessing proceeds to step 1480.

When the processing proceeds to step 1480, the CPU multiplies thereference lower limit vehicle speed SLnowb by the correctioncoefficients kR, kL, kW, kN, and kH in accordance with the followingequation (1) and thereby corrects the reference lower limit vehiclespeed SLnowb to compute the lower limit vehicle speed SLnow. Then theprocessing proceeds to step 1350 in FIG. 13. The lower limit vehiclespeed

SLnow=kR·kL·kW·kN·kH·SLnowb  (1)

According to this fifth modified example apparatus, the lower limitvehicle speed SLnow is corrected to be increased in the case where thehost vehicle is less likely to be recognized by the driver of thevehicle behind (in the case of the poor visibility), such as the casewhere the roadside wall exists on the side to which the host vehicleturns on the curved road, the case of the bad weather, the case of thenighttime, or the case where the vehicle height H of the host vehicle islow. As a result, a possibility that the driver of the vehicle behindhas to abruptly brake the vehicle behind when recognizing the hostvehicle can further reliably be reduced. Note that the values d1, d2,d3, d4, and d5 may differ or be the same.

Sixth Embodiment

A description will next be made on a vehicle travel control apparatus(hereinafter may be referred to as a “sixth apparatus”) according to asixth embodiment of the disclosure. When determining that the driver isin the driving incapable abnormal state, the sixth apparatus deceleratesthe host vehicle at the constant deceleration Dec and obtains thecurrent position Pnow of the host vehicle and a position Ptg of a passof the road on which the host vehicle currently travels (a point where agrade changes from an up grade to a down grade) from the GPS receiver 21and the map database 22 via the navigation ECU 20.

When the vehicle travels on the road with the up grade in front of apoint of the pass, the driver of the vehicle has difficulty in visuallyrecognizing a situation ahead of the point of the pass. That is, thedriver has the poor visibility in front of the pass as on the curvedroad. Accordingly, in the case where the vehicle whose driver has beendetermined to be in the driving incapable abnormal state (thedeceleration target vehicle) and which has forcibly been decelerated asa result travels at the excessively low vehicle speed at a point aheadof the point of the pass, the driver of the vehicle behind has toabruptly brake the vehicle behind after the vehicle behind passes thepoint of the pass and the driver of the vehicle behind recognizes thevehicle. Furthermore, timing at which the driver of the vehicle behindfirst recognizes the deceleration target vehicle that passes the pass isdelayed longer as a difference between a road grade immediately beforethe pass and a road grade immediately after the pass (a grade changeamount) is increased.

Based on such a viewpoint, the sixth apparatus obtains the grade changeamount of the pass that the deceleration target vehicle has passed fromthe map database 22 via the navigation ECU 20 and sets the lower limitvehicle speed on the basis of the grade change amount. Furthermore, thesixth apparatus computes a distance D for which the deceleration targetvehicle has traveled after passing the point of the pass, and correctsto increase the lower limit vehicle speed as the distance D is reduced.

Then, in the case where the vehicle speed SPD becomes equal to or lowerthan the lower limit vehicle speed SPDmin, the sixth apparatustemporarily stops the deceleration to make the vehicle travel at theconstant speed (that is, keeps the vehicle speed) or accelerates thehost vehicle at the constant acceleration until the vehicle speedmatches the lower limit vehicle speed SPDmin. In this way, in the casewhere the driver of the vehicle behind recognizes the decelerationtarget vehicle when the vehicle behind passes the point of the pass, thedriver of the vehicle behind can decelerate or stop the vehicle behindwithout abruptly braking the vehicle behind. What has been described sofar is the overview of actuation of the sixth apparatus.

(Specific Actuation) Next, a description will be made on specificactuation of the CPU in the ECU 10 according to the sixth apparatus. TheCPU executes the routines shown in the flowcharts of FIG. 15 whichreplaces FIG. 3, FIG. 4, and FIG. 5 every time a specified time elapses.Because the flowcharts of FIG. 4 and FIG. 5 have already been described,a description will hereinafter be made on actuation (vehicledeceleration processing) based on the flowchart of FIG. 15.

At specified timing, the CPU starts the processing from step 1500 inFIG. 15, the processing proceeds to step 1510, and the CPU determineswhether the value of the driver abnormality occurrence flag Xijo is “1”.If the value of the flag Xijo is not “1”, the CPU determines “No” instep 1510, the processing directly proceeds to step 1595, and thisroutine is terminated once. Thus, in this case, the host vehicle is notforcibly decelerated.

On the other hand, if the value of the driver abnormality occurrenceflag Xijo is “1” at a time point at which the CPU executes theprocessing in step 1510, the CPU determines “Yes” in 1510, theprocessing proceeds to step 1520, and the CPU determines whether thevehicle speed SPD is higher than “0”. If the vehicle speed SPD is “0”,the CPU determines “No” in step 1520. Then, the processing directlyproceeds to step 1595, and this routine is terminated once.

On the other hand, if the vehicle speed SPD is higher than “0”, the CPUdetermines “Yes” in step 1520, and the processing proceeds to step 1530.The CPU obtains the position Pnow of the host vehicle at the currenttime point, the position Pold of the host vehicle before the specifiedtime, and the position Ptg of the pass of the road on which the hostvehicle currently travels from the navigation ECU 20. Then, based onthese, the CPU determines whether the host vehicle has passed theposition Ptg of the pass of the road. If the host vehicle has not passedthe position Ptg of the pass of the road, the CPU determines “No” instep 1530. Then, the processing directly proceeds to step 1595, and thisroutine is terminated once.

On the other hand, if the host vehicle has passed the position Ptg ofthe pass of the road, the CPU determines “Yes” in step 1530 andsequentially executes processing from step 1535 to step 1570, which willbe described below, and the processing proceeds to step 1580. Note thatin the case where the CPU executes the processing in step 1530immediately after the host vehicle passes the position Ptg of the passof the road, the CPU sets the travel distance D, which will be describedbelow, to “0”.

Step 1535: The CPU obtains a road grade Ib (Ib>0) immediately before theposition Ptg of the pass and a road grade Ia (Ia<0) immediately afterthe position Ptg of the pass from the map database 22 via the navigationECU 20 and obtains a difference therebetween (that is, a grade changeamount) dI (=Ib−Ia). Step 1540: The CPU determines a reference lowerlimit vehicle speed SPDminb by applying the grade change amount dI to alookup table MapSPDminb(dI) shown in a block B4 of FIG. 15. According tothis table MapSPDminb(dI), the reference lower limit vehicle speedSPDminb is computed to be increased as the grade change amount dI isincreased.

Step 1550: Based on the position Ptg of the pass and the position Pnowof the host vehicle, the CPU obtains the distance (the travel distance)D for which the host vehicle has traveled from the position Ptg of thepass. Step 1560: The CPU determines a correction coefficient kd byapplying the travel distance D to a lookup table Mapkd(D) shown in ablock B5 of FIG. 15. According to this table Mapkd(D), the correctioncoefficient kd is computed to be reduced as the travel distance D isincreased. The correction coefficient kd becomes “0” when the traveldistance becomes equal to or longer than a threshold distance. Step1570: The CPU obtains the lower limit vehicle speed SPDmin bymultiplying the reference lower limit vehicle speed SPDminb by thecorrection coefficient kd.

Next, the processing proceeds to step 1580, and the CPU determineswhether the vehicle speed SPD at the current time point is higher thanthe lower limit vehicle speed SPDmin. If the vehicle speed SPD at thecurrent time point is higher than the lower limit vehicle speed SPDmin,the CPU determines “Yes” in step 1580, the processing proceeds to 1585,and the CPU decelerates the host vehicle at the constant decelerationDec. Thereafter, the processing proceeds to step 1595, and this routineis terminated once.

On the other hand, if the vehicle speed SPD at the current time point isequal to or lower than the lower limit vehicle speed SPDmin, the CPUdetermines “No” in step 1580, the processing proceeds to step 1590, andthe CPU temporarily stops the deceleration at the constant decelerationDec. In addition, if the vehicle speed SPD at the current time point isequal to the lower limit vehicle speed SPDmin, the CPU makes the hostvehicle travel at the constant speed. If the vehicle speed SPD at thecurrent time point is lower than the lower limit vehicle speed SPDmin,the CPU accelerates the host vehicle at the constant acceleration Accuntil the vehicle speed SPD of the host vehicle matches the lower limitvehicle speed SPDmin. Thereafter, the processing proceeds to step 1595,and this routine is terminated once.

As it has been described so far, the sixth apparatus obtains informationon the change amount of the road grade (Ia, Ib) on which thedeceleration target vehicle travels as the information on the roadshape, and sets the lower limit vehicle speed to the higher value as thegrade change amount (dI) at the point of the pass, which is indicated bythe info, illation on the grade change amount, is increased. Then, thesixth apparatus controls the vehicle speed of the deceleration targetvehicle such that the vehicle speed of the deceleration target vehicledoes not become lower than the lower limit vehicle speed. Furthermore,the sixth apparatus increases the lower limit vehicle speed as thetravel distance of the deceleration target vehicle from the point of thepass is reduced.

In the case where the deceleration target vehicle travels by passing thepass at which the road grade is changed from the up grade to the downgrade, the timing at which the driver of the vehicle behind recognizesthe deceleration target vehicle is delayed longer as the grade changeamount before and after the pass is increased. Accordingly, when thelower limit vehicle speed is set on the basis of the grade change amountas by the sixth apparatus, a “possibility that the driver of the vehiclebehind has to abruptly brake the vehicle behind” due to the decelerationtarget vehicle can be reduced.

Note that, like the first apparatus to the third apparatus, the sixthapparatus may handle the lower limit vehicle speed that is increasedimmediately after the deceleration target vehicle passes the point ofthe pass in a similar manner to the lower limit vehicle speed based onthe radius of curvature. That is, the first to the third apparatus mayhandle higher one of the lower limit vehicle speed that is based on theradius of curvature and is taken into consideration thereby and thelower limit vehicle speed that is increased immediately after thedeceleration target vehicle passes the point of the pass as the lowerlimit vehicle speed. Furthermore, in the case where an accelerationsensor that can detect an inclination of the host vehicle is mounted,the sixth apparatus may determine whether the host vehicle has passedthe point of the pass on the basis of a detection value of theacceleration sensor. Moreover, the sixth apparatus may compute the abovedistance D by “integrating the vehicle speed SPD obtained from thevehicle speed sensor 16”.

Seventh Embodiment

Next, a description will be made on a vehicle travel control apparatus(hereinafter may be referred to as a “seventh apparatus”) according to aseventh embodiment of the disclosure. The seventh apparatus differs fromthe first apparatus only in a point that the seventh apparatus makes thedriver abnormality determination by using the confirmation button 90. Adescription will hereinafter be centered on this different point. Notethat a driver abnormality determination method of the seventh apparatuscan also be applied to the other vehicle travel control apparatuses suchas the second to the sixth apparatuses.

(Specific Actuation) The CPU of the ECU 10 according to the seventhapparatus executes a routine shown in a flowchart of FIG. 16 every timethe specified time elapses. Accordingly, at specified timing, the CPUstarts the processing from step 1600 of FIG. 16, the processing proceedsto step 1610, and the CPU determines whether the value of the driverabnormality occurrence flag Xijo is “0”. As described above, the valueof the flag Xijo is set to “0” in the initial routine.

If the value of the driver abnormality occurrence flag Xijo is “1”, theCPU determines “No” in step 1610, the processing directly proceeds tostep 1695, and this routine is terminated once.

On the other hand, if the value of the driver abnormality occurrenceflag Xijo is “0”, the CPU determines “Yes” in step 1610, the processingproceeds to step 1620, and the CPU determines whether a first time haselapsed from a time point at which actuation for urging an operation ofthe confirmation button 90 is performed (an urging time point). If thefirst time has not elapsed from the urging time point, the CPUdetermines “No” in step 1620. Then, the processing directly proceeds tostep 1695, and this routine is terminated once.

On the other hand, if the first time has elapsed from the urging timepoint, the CPU determines “Yes” in step 1620, the processing proceeds tostep 1630, and the CPU urges the operation of the confirmation button90. More specifically, by using the alarm ECU 80, the CPU displays amessage of such intent, “Please press the confirmation button 90.”, onthe indicator 82 and intermittently sounds the buzzer 81. In this way,unless the driver falls in the driving incapable abnormal state, thedriver usually operates (presses, that is, turns on) the confirmationbutton 90.

Next, the processing proceeds to step 1640, and the CPU deter mineswhether the confirmation button 90 has been operated. If theconfirmation button 90 has been operated, the CPU determines “Yes” instep 1640, the processing proceeds to step 1650, and the CPU sets(clears) a value of a counter Cnt to “0”. Then, the processing proceedsto step 1695, and this routine is terminated once.

On the other hand, if the confirmation button 90 has not been operatedat a time point at which the CPU executes the processing in step 1640,the CPU determines “No” in step 1640, the processing proceeds to step1660, and the CPU determines whether a second time has elapsed from thetime point at which the CPU urges the operation of the confirmationbutton 90 (that is, a time point at which the processing in step 1630 isexecuted). The second time is set as a shorter time than the first time.

If the second time has not elapsed from the time point at which the CPUurges the operation of the confirmation button 90, the CPU determines“No” in step 1660, and the processing returns to step 1640. Accordingly,the CPU monitors whether the confirmation button 90 is operated in aperiod from the time point at which the CPU urges the operation of theconfirmation button 90 to a lapse of the second time.

If the confirmation button 90 is not operated in the period from thetime point at which the CPU urges the operation of the confirmationbutton 90 to the lapse of the second time, the CPU determines “Yes” instep 1660, the processing proceeds to step 1670, and the CPU increases avalue of the counter Cnt by “1”. Note that the CPU temporarily stopsurging the operation of the confirmation button 90 at this time.

Next, the processing proceeds to step 1680, and the CPU deter mineswhether the value of the counter Cnt is equal to or larger than athreshold Cnth that corresponds to a threshold time. If the value of thecounter Cnt is smaller than the threshold Cnth, the CPU determines “No”in step 1680. Then, the processing directly proceeds to step 1695, andthis routine is terminated once. In this case, when the first timeelapses, the CPU executes the processing in step 1630 onward again.

Just as described, in the case where the driver falls in the drivingincapable abnormal state, the confirmation button 90 is not operatedeven when the operation of the confirmation button 90 is urged everytime the first time elapses. As a result, the value of the counter Cntis increased in step 1670 and becomes equal to or larger than thethreshold Cnth. In this case, the CPU determines “Yes” in step 1680, theprocessing proceeds to step 1690, and the CPU sets the value of thedriver abnormality occurrence flag Xijo to “1”. In other words, the CPUconfirms such a determination that the driver is in the drivingincapable abnormal state.

Next, the processing proceeds to step 1692, and the CPU prohibits theacceleration override. That is, the CPU prohibits the acceleration(including the deceleration) of the vehicle based on the change in theaccelerator pedal operation amount AP (disables an acceleration requestbased on the operation of the accelerator pedal) at this time point (theabnormality determination time point) onward. Thereafter, the processingproceeds to step 1695, and this routine is terminated once.

As it has been described so far, the vehicle travel control apparatusaccording to each of the embodiments and the modified example of thedisclosure decelerates the deceleration target vehicle such that thevehicle speed thereof does not fall below the lower limit vehicle speed,and the lower limit vehicle speed is set on the basis of the road shapethat influences the timing (delays the timing) at which the driver ofthe vehicle behind the deceleration target vehicle visually recognizesthe deceleration target vehicle. Thus, the possibility that the driverof the vehicle behind has to abruptly brake the vehicle behind due tothe deceleration target vehicle can be reduced. In addition, theabove-described embodiments may be combined within the scope that doesnot produce any discrepancy.

The disclosure is not limited to the above embodiments and modifiedexample, and various modifications can be adopted therefor within thescope of the disclosure. For example, as abnormality determination meansthat makes the driver abnormality determination (the processing ofdetermining whether the value of the driver abnormality occurrence flagXijo is set to “1”), a so-called “driver monitoring technique” disclosedin JP 2013-152700 A may be adopted. More specifically, an image of thedriver is captured by using a camera that is provided on a member (forexample, a steering wheel, a pillar, and the like) in a vehicle cabin,and a direction of eyesight or a direction of a face of the driver ismonitored by using the captured image. Then, in the case where thedirection of the eyesight or the direction of the face of the drivercontinues to correspond to a direction in which the eyesight or the faceof the driver does not face for a long time during a normal operation ofthe vehicle for a time that is equal to or longer than the specifiedtime, the determination that the driver is in the driving incapableabnormal state may be confirmed, and the value of the flag Xijo may beset to “1”.

Furthermore, the map database 22 may be mounted on a facility outside ofthe vehicle (a traffic center) or the like. In this case, each of thevehicle travel control apparatuses according to the embodiments of thedisclosure may obtain the information on the road shape (the radius ofcurvature, the road grade, and the like) by using the communicationdevice, which is not shown.

Moreover, of the vehicle travel control apparatuses according to theembodiments of the disclosure, the apparatus that obtains theinformation on the road shape from the map database 22 may directlyobtain the “lower limit vehicle speed corresponding to the road shape”,which is set per section of the road in advance, from the map database22 instead of the information on the road shape.

The vehicle travel control apparatuses according to the embodiments ofthe disclosure may make the driver abnormality determination only whenboth of the lane keeping assist control and the adaptive cruise controlare executed through the operation of the operation switch 18 by thedriver. Note that the adaptive cruise control is control that makes thehost vehicle follow the preceding vehicle while keeping theinter-vehicular distance between the preceding vehicle that travelsright in front of the host vehicle and the host vehicle to a specifieddistance on the basis of the target object information obtained by theradar sensor 17 a and the camera device 17 b. Because the adaptivecruise control itself is well known, the description thereon will not bemade (for example, see Japanese Patent Application Publication No.2014-148293 (JP 2014-148293 A), Japanese Patent Application PublicationNo. 2006-315491 (JP 2006-315491 A), the specification of Japanese PatentNo. 4172434, the specification of Japanese Patent No. 4929777, and thelike).

An example of the driver abnormality determination method in the casewhere both of lane keeping assist control and the adaptive cruisecontrol are executed is as follows. For example, when an operation inwhich the steering wheel is not maneuvered and thus the steering torqueTra is zero (“0”) continues for a first specified time (Tath: forexample, five seconds), the vehicle travel control apparatus tentativelydetermines that the driver possibly falls in the driving incapableabnormal state. At this time, the vehicle travel control apparatusstarts decelerating the host vehicle at the extremely low decelerationfrom this state. Then, when a state where neither the accelerator pedaloperation amount AP nor the steering torque Tra is changed therebycontinues for a second specified time (Tbth: for example, 30 seconds to1 minute), the vehicle travel control apparatus confirms thedetermination that the driver falls in the driving incapable abnormalstate.

What is claimed is:
 1. A vehicle travel control apparatus comprising: atleast one actuator; and at least one electronic control unit configuredto determine whether a driver of a vehicle is in an abnormal state wherethe driver loses an ability of driving the vehicle, stop the vehicle atan abnormality determination time point onward, the abnormalitydetermination time point being a time point at which it is determinedthat the driver is in the abnormal state, and control a vehicle speed ofthe vehicle by using the at least one actuator such that the vehiclespeed does not become lower than a lower limit vehicle speed, in aperiod from the abnormality determination time point to a time point atwhich the vehicle is stopped, the lower limit vehicle speed being set inaccordance with a road shape, the road shape influencing timing at whicha driver of another vehicle traveling behind the vehicle visuallyrecognizes the vehicle, the road shape being among shapes of the road onwhich the vehicle travels.
 2. The vehicle travel control apparatusaccording to claim 1, wherein the at least one electronic control unitis configured to obtain information on the road shape, and set the lowerlimit vehicle speed based on the information on the road shape.
 3. Thevehicle travel control apparatus according to claim 2, wherein the atleast one electronic control unit is configured to obtain information ona radius of curvature of the road at a point ahead of a point at whichthe vehicle travels at a current time point as the information on theroad shape, and set the lower limit vehicle speed to a higher value asthe radius of curvature indicated by the information on the radius ofcurvature is reduced.
 4. The vehicle travel control apparatus accordingto claim 3, wherein the at least one electronic control unit isconfigured to obtain the radius of curvature or the curvature of atleast one section of the road as information on the radius of curvatureof the road from a map database, set the lower limit vehicle speed foreach of the section based on the radius of curvature or the curvature ofeach of the section, determine a particular point reaching time point,the particular point reaching time point being determined such that thevehicle speed of the vehicle in a period from the particular pointreaching time point to the time point at which the vehicle is stoppeddoes not become lower than the lower limit vehicle speed, the particularpoint reaching time point being at which the vehicle reaches aparticular point ahead of a position at the abnormality determinationtime point, the lower limit vehicle speed being set for each of thesection, when the vehicle reaches the particular point reaching timepoint while keeping a vehicle speed at the abnormality determinationtime point, and the vehicle is decelerated at constant deceleration fromthe particular point reaching time point, and make the vehicle travel atthe vehicle speed at the abnormality determination time point, from theabnormality determination time point to the particular point reachingtime point, and decelerate by using the at least one actuator thevehicle at the constant deceleration from the particular point reachingtime point.
 5. The vehicle travel control apparatus according to claim3, wherein the at least one electronic control unit is configured toobtain the radius of curvature or the curvature of at least one sectionof the road as the information on the radius of curvature of the roadfrom a map database, set the lower limit vehicle speed for each of thesection based on the radius of curvature or the curvature of each of thesection, determine constant deceleration such that the vehicle speed ofthe vehicle in the period from the abnormality determination time pointto the time point at which the vehicle is stopped does not become lowerthan the lower limit vehicle speed set for each of the section when thevehicle is decelerated at the constant deceleration from the abnormalitydetermination time point, and decelerate the vehicle at the constantdeceleration by using the at least one actuator from the abnormalitydetermination time point.
 6. The vehicle travel control apparatusaccording to claim 3, wherein the at least one electronic control unitis configured to obtain the radius of curvature or the curvature of atleast one section as the information on the radius of curvature of theroad from a map database, set the lower limit vehicle speed for each ofthe section based on the radius of curvature or the curvature of each ofthe section, decelerate the vehicle at constant deceleration at theabnormality determination time point onward, and temporarily interruptdeceleration of the vehicle and keep the vehicle speed of the vehicle ina period in which it is predicted that the vehicle speed of the vehiclebecomes lower than the lower limit vehicle speed set for each of thesection, the period being in the period from the abnormalitydetermination time point to the time point at which the vehicle isstopped.
 7. The vehicle travel control apparatus according to claim 3further comprising: a camera device that obtains image data by capturingan image in front of the vehicle, wherein the at least one electroniccontrol unit is configured to obtain the radius of curvature or thecurvature of the road at a particular point ahead of a position of thevehicle at the current time point by a specified distance as theinformation on the radius of curvature of the road based on the imagedata, and set the lower limit vehicle speed based on the radius ofcurvature or the curvature at the particular point, and in a case whereit is predicted that the vehicle speed at a time when the vehiclereaches the particular point becomes lower than the lower limit vehiclespeed when the vehicle is decelerated at constant deceleration from theabnormality determination time point onward, the at least one electroniccontrol unit is configured to make the vehicle travel at a constantspeed so as to keep the vehicle speed of the vehicle at a time pointwhen the vehicle speed is predicted, in a case where the vehicle speedof the vehicle at the time point when the vehicle speed is predicted isequal to or higher than the lower limit vehicle speed at the particularpoint, and accelerate the vehicle by using the at least one actuatorsuch that the vehicle speed of the vehicle becomes equal to or higherthan the lower limit vehicle speed at the particular point before thevehicle reaches the particular point in a case where the vehicle speedof the vehicle at the time point when the vehicle speed is predicted islower than the lower limit vehicle speed at the particular point.
 8. Thevehicle travel control apparatus according to claim 2, wherein the atleast one electronic control unit is configured to obtain information ona radius of curvature of the road at a point at which the vehicletravels at a current time point as the information on the road shape,and set the lower limit vehicle speed to a higher value as the radius ofcurvature indicated by the information on the radius of curvature isreduced.
 9. The vehicle travel control apparatus according to claim 8further comprising: a camera device that obtains image data by capturingan image in front of the vehicle, wherein the at least one electroniccontrol unit is configured to obtain the radius of curvature or thecurvature of the road at the point at which the vehicle travels at thecurrent time point as the information on the radius of curvature of theroad based on the image data, decelerate the vehicle when the vehiclespeed of the vehicle at the current time point is higher than the lowerlimit vehicle speed at the point at which the vehicle travels at thecurrent time point, and accelerate the vehicle by using the at least oneactuator such that the vehicle speed of the vehicle becomes equal to orhigher than the lower limit vehicle speed, when the vehicle speed of thevehicle at the current time point is lower than the lower limit vehiclespeed at the point at which the vehicle travels at the current timepoint.
 10. The vehicle travel control apparatus according to claim 2,wherein the at least one electronic control unit is configured to obtaininformation on a grade change amount of the road as the information onthe road shape, and set the lower limit vehicle speed to a higher valueas the grade change amount at a point of a pass, the point of the passbeing indicated by the information on the grade change amount, isincreased.
 11. The vehicle travel control apparatus according to claim10, wherein the at least one electronic control unit is configured toobtain the information on the grade change amount from a map database,and set the lower limit vehicle speed to a higher value as the gradechange amount is increased.
 12. The vehicle travel control apparatusaccording to claim 10, wherein the at least one electronic control unitis configured to obtain a travel distance for which the vehicle travelsafter passing the point of the pass, and set the lower limit vehiclespeed to a higher value as the travel distance is reduced.
 13. Thevehicle travel control apparatus according to claim 1, wherein the atleast one electronic control unit is configured to determine that thedriver of the vehicle is in the abnormal state when the driver of thevehicle does not perform a predetermined operation for a longer timethan a predetermined time.
 14. The vehicle travel control apparatusaccording to claim 13, wherein the at least one electronic control unitis configured to determine that the driver of the vehicle is in theabnormal state when the driver of the vehicle does not perform a driveoperation for the longer time than the predetermined time.
 15. Thevehicle travel control apparatus according to claim 13 furthercomprising: a confirmation button mounted on the vehicle, wherein the atleast one electronic control unit is configured to make notification ofurging the driver of the vehicle to operate the confirmation button, anddetermine that the driver of the vehicle is in the abnormal state whenthe driver of the vehicle does not operate the confirmation button for apredetermined time after the notification is made.